English

• 1.   Introduction

  β-Ketophosphine oxides are a class of versatile organophosphorus compounds, which exhibit a wide range of applications in many areas such as valuable synthetic intermediates for the construction of α, β-unsaturated carbonyl compounds, ^[1] potential bidentate ligands, ^[2] and transition elements extractants.^[3] Therefore, this has led to the increasing interest in the development of novel synthetic strategies for affording β-ketophosphine oxides in recent years. In particular, one of the most powerful tools is organophosphorus radical-triggered phosphorylation reaction of various radical acceptors, including alkenes, ^[4] alkynes, ^[5] cinnamic/alkynyl carboxylic acids, ^[6] cinnamyl/alkynyl carboxylates, ^[7] α, β-unsaturated carbonyl or 1, 3-dicarbonyl compounds, ^[8] vinyl azides, ^[9] ketone O-acetyl oximes or α-substituted olefins generated from ketones.^[10] A great feature of these methods is to realize the transformation of various functional moieties into β-ketophosphine oxide scaffolds. However, despite considerable progress, the development of mild, convenient, efficient methods to access β-ketophosphine oxides via the phosphorylation of radical acceptors containing other functional moieties is still highly desirable.

  2-Substituted acrylates, a kind of important and readily-available electron-deficient alkenes, have drawn much attention for their application as a potential radical acceptor for the construction of structurally diverse esters.^[11] Very recently, we disclosed a simple and practical coppercatalyzed direct hydroxyphosphorylation of 2-substituted acrylates with H-phosphine oxides to access β-hydroxy-phosphine oxides (Scheme 1).^[11k] At the same time, one deesterificative oxyphosphorylation byproduct β-ketophos- phine oxide was unexpectedly formed. As we know, selective catalysis affording diverse products from the same starting materials is a powerful tool for divergent synthesis.^[12] Therefore, in order to let the more valuable byproduct β-ketophosphine oxide become as major one, we wish to control the product selectivity by the modification of the reaction conditions. To the best of our knowledge, an example on β-ketophosphine oxide formation through deesterificative oxyphosphorylation of 2-substituted acrylates is yet to be reported. In continuation of our interest in difunctionalization of unsaturated hydrocarbons and the construction of organophosphorus compounds, ^[13] we report herein an efficient, selective and practical process for the synthesis of β-ketophosphine oxides via hydrochloric acid-promoted copper/iron-cocatalyzed deesterificative oxyphosphorylation of 2-substituted acrylates with H-phos- phine oxides and dioxygen (Scheme 1).

  Scheme 1

  

  Scheme 1.  Phosphorylation of 2-substituted acrylates

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  2.   Results and discussion

  We commenced our study by investigating the reaction between ethyl 2-phenylacrylate (1a) and diphenylphosphine oxide (2a) in order to generate a deesterificative oxyphosphorylation product, and the results are summarized in Table 1. Firstly, only low yields were obtained for the desired product 3a when the reaction temperature was elevated to 40 or 60 ℃ under the standard conditions for the synthesis of β-hydroxyphosphine oxides according to our previous report (Entries 1, 2).^[11k] Gratifyingly, reaction efficiency was significantly improved when the model reaction was performed at 40 ℃ for 3 h by using hydrochloric acid (aq., 1 mol/L) instead of Et₃N, indicating that acid could efficiently promote the deesterificative oxyphosphorylation of 2-substituted acrylates and suppress the direct hydroxyphosphorylation reaction (Entries 3, 4). Encouraged by this result, a variety of acids were examined, and the results showed that hydrochloric acid (aq., 1 mol/L) was the most suitable additive to promote the model reaction (Entries 5~10). To further improve the yield, other copper salts such as CuCl₂, CuBr, Cu(OTf)₂ and Cu(acac)₂ were examined, among which CuBr₂ was found to be still the most efficient catalyst (Entries 11~14). When a cocatalyst including Ag, Pd, Au and Fe salt was introduced into the reaction system, and Fe salts, especially FeCl₃, were found to be the optimal cocatalyst, with the yield of 3a being improved to 77% (Entries 15~20). However, a significantly lower yield of 3a was obtained when the reaction was performed in the absence of the copper salt, suggesting that copper/iron-cocatalysis was one of the essential prerequisites for this deesterificative oxyphosphorylation (Entry 21). After an extensive screening of the reaction parameters (see Table 1 and the Supporting Information), the best yield of 3a (77%) was obtained by employing 1a (0.5 mmol), 2a (1.0 mmol), CuBr₂ (5 mol%), FeCl₃ (10 mol%), and HCl (aq., 0.15 mmol, 1 mol/L) in N, N-dimethylformamide (DMF) at 40 ℃ for 3 h under an oxygen atmosphere (Entry 19).

  Table 1

  

  Table 1.  Optimization of reaction conditions^a

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  Entry	Catal.	Cocatal.	Additive	Yieldb/%
  1	CuBr2	-	Et3N	19c
  2	CuBr2	-	Et3N	21d
  3	CuBr2	-	-	22
  4	CuBr2	-	HCl (aq., 1 mol/L)	49
  5	CuBr2	-	HCOOH	29
  6	CuBr2	-	CH3COOH	27
  7	CuBr2	-	PhCH2COOH	24
  8	CuBr2	-	Salicylic acid	22
  9	CuBr2	-	PhB(OH)2	31
  10	CuBr2	-	TsOH	21
  11	CuCl2	-	HCl (aq., 1 mol/L)	45
  12	CuBr	-	HCl (aq., 1 mol/L)	42
  13	Cu(OTf)2	-	HCl (aq., 1 mol/L)	34
  14	Cu(acac)2	-	HCl (aq., 1 mol/L)	38
  15	CuBr2	AgCl	HCl (aq., 1 mol/L)	39
  16	CuBr2	PdCl2	HCl (aq., 1 mol/L)	40
  17	CuBr2	AuCl3	HCl (aq., 1 mol/L)	42
  18	CuBr2	FeBr3	HCl (aq., 1 mol/L)	74
  19	CuBr2	FeCl3	HCl (aq., 1 mol/L)	77
  20	CuBr2	FeCl2	HCl (aq., 1 mol/L)	51
  21	-	FeCl3	HCl (aq., 1 mol/L)	54

  Under the optimized reaction conditions, the substrate scope and limitations of this deesterificative oxyphosphorylation were investigated. As demonstrated in Table 2, phenethyl 2-phenylacrylate as substrate could also give the desired product 3a in 71% yield. Generally, a variety of 2-arylacrylate and its derivatives with electron-donating or electron-withdrawing substituents at the ortho-, meta- or para-positions of the phenyl rings were suitable for this protocol, affording the corresponding desired products 3b~3q in moderate to good yields. Notably, various functional groups, such as methoxy (3b, 3c), halogens (3g~3m), trifluoromethyl (3n), ester (3o), cyano (3p) and nitro (3q), were found to be well tolerated in this oxyphosphorylation transformation. Furthermore, ethyl 2-(naphthalen-2- yl)acrylate and ethyl 3-(pyridin-2-yl)acrylate were also good candidates in the present reaction and gave the corresponding desired products 3r~3s in 67% and 86% yields, respectively. However, 2-alkylacrylate derivatives such as methyl methacrylate and 3-methylenedihydro-2(3H)- furanone could generate the corresponding target products 3t~3u with relatively low yields of 24% and 35%.

  Table 2

  

  Table 2.  Screening of substrate scope^a, ^b

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  a Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), CuBr2 (5 mol%), FeCl3 (10 mol%), HCl (aq., 0.15 mmol, 1 mol/L), DMF (2.0 mL), O2 (balloon), 40 ℃, 3 h. b Isolated yields based on 1. c Phenethyl 2-phenylacrylate instead of ethyl 2-phenylacrylate. d The hydroxyphosphorylation product 3t' was obtained in 36% yield. e Reaction conditions: Et3N (0.5 mmol) instead of HCl (aq., 0.15 mmol, 1 mol/L).

  Next, the scope of this deesterificative oxyphosphorylation was further expanded to other H-phosphine oxides. In addition to diphenylphosphine oxide (2a), methyl-, methoxy-, and fluoro-substituted diphenylphosphine oxides could also be converted into the corresponding β-ketophosphine oxides 3v~3x in good yields. Nevertheless, when diethyl phosphonate was used as substrate, no desired product 3y was observed under the optimized conditions due to its low reactivity. Pleasingly, when 1.0 equiv. of Et₃N was added instead of hydrochloric acid (aq., 1 mol/L), β-ketophosphonate 3y was successfully afforded in a satisfactory yield.

  To showcase the practical utility of the deesterificative oxyphosphorylation of 2-substituted acrylates, the model reaction between 1a and 2a was performed on a gram scale under the optimized conditions. As shown in Eq. 1, β-ketophosphine oxide 3a could be obtained in a satisfactory yield of 71% (2.27 g).

  (1)

  To rationalize the mechanism for the deesterificative oxyphosphorylation of 2-substituted acrylates, several control experiments were performed (Scheme 2). No reaction occurred when only ethyl 2-phenylacrylate (1a) or β-hydroxyphosphine oxide (5a) was employed under the optimized conditions, which implied that the possibility of the direct conversion of 4a or 5a into 3a could be fully excluded in the present oxyphosphorylation (Scheme 2). Subsequently, the model reaction was almost suppressed by the addition of 2, 2, 6, 6-tetramethyl-1-piperidinyl-oxy (TEMPO) as a radical scavenger, indicating that this transformation might involve a radical pathway (Scheme 2). Furthermore, a relatively lower yield of the target product 3a (51%) could also be obtained under an air atmosphere, but none of 3a was observed when O₂ was replaced by N₂, suggesting that molecular dioxygen was indispensable for this process (Scheme 2).

  Scheme 2

  

  Scheme 2.  Control experiments

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  Based on the aforementioned results, preceding mechanistic studies, ^{[4a, 11k, 14]} and LC-HRMS analysis (see the Supporting Information), a tentative mechanism of this deesterificative oxyphosphorylation was proposed accordingly as indicated in Scheme 3. It was well known that the copper(Ⅱ) species could be oxidized to the more electrophilic copper(Ⅲ) species in the presence of iron(Ⅲ). Initially, the reaction proceeded by a single electron transfer (SET) from Ph₂P(O)H (2a) to copper(Ⅱ/Ⅲ) species and concomitant proton transfer (PT) under O₂, affording corresponding phosphorus radical A and Cu^Ⅱ/Ⅲ-(•OOH) species. Then, the regioselective addition of phosphorus radical A to ethyl 2-phenylacrylate (1a) generated a reactive alkyl radical B, which interacted with Cu^Ⅱ/Ⅲ-(•OOH) species to give hydroperoxide intermediate C. With the help of acid, the resulting intermediate C could in situ generate a dioxetanone D through the intramolecular ester exchange, which subsequently underwent decarboxylation process to release CO₂ and the final product 3a, along with peroxide cleavage. In particular, intermediates C and D were detected by LC-HRMS in the developed reaction system.

  Scheme 3

  

  Scheme 3.  Tentative reaction mechanism

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  3.   Conclusions

  In summary, an unprecedented copper/iron-cocatalyzed deesterificative oxyphosphorylation of 2-substituted acrylates with H-phosphine oxides and dioxygen has been developed for the construction of β-ketophosphine oxides. In this methodology, a cheap and readily available hydrochloric acid is employed to promote the deesterification oxyphosphorylation process and inhibit the preceding hydroxylphosphorylation process. The developed protocol provides a selective and practical method for the synthesis of a library of valuable β-ketophosphine oxides with a wide range of substrate scope and good functional group tolerance under mild conditions by using readily available starting materials, along with chemoselective cleavage of C(sp²)—C(C=O) bonds. A tentative radical-initiated mechanism is proposed on the basis of preliminary mechanistic studies. Further detailed mechanism and synthetic applications of this methodology are ongoing in our laboratory.

  4.   Experimental section

  4.1   Instruments and agents

  ¹H NMR, ¹³C NMR and ³¹P NMR were recorded in CDCl₃ on a bruker advance Ⅲ 400 M NMR with tetramethylsilane (TMS) as internal standard at room temperature. HRMS and LC-HRMS analyses were obtained on a Waters Vion^® IMS QT of mass spectrometer and a Waters UPLC-Xevo TQ MS (PDA Detector)/Waters Vion^® IMS QT of mass spectrometer by ESI method, respectively. Flash column chromatography was carried out on silica gel (100~200 mesh). All solvents were purified by standard methods. All chemicals were purchased from TCI, J & K and Energy chemical companies, and used without further purification. The 2-substituted acrylates and H-phosphine oxides were stored at 4 ℃ before used.

  4.2   Synthesis of compound 3

  2-Substituted acrylate (0.5 mmol) was added to a 50 mL round-bottom flask with H-phosphine oxide (1.0 mmol), CuBr₂ (6 mg, 5 mol%), FeCl₃ (8 mg, 10 mol%), HCl (aq., 0.15 mmol, 1 mol/L) in DMF (2 mL) at 40 ℃ under O₂ (balloon). The reaction mixture was stirred for 3 h. Upon completion of the reaction, saturated sodium bicarbonate solution (10 mL) was added to the reaction mixture, and the resulting mixture was extracted with ethyl acetate (8 mL×3). The combined organic layers were washed with water (8 mL×2) and brine (8 mL×2), dried over anhydrous sodium sulfate, filtered, concentrated under reduced pressure, and purified by flash column chromatography using petroleum ether/ethyl acetate (V/V=3:1~1:2) to provide the corresponding product.

  2-(Diphenylphosphoryl)-1-phenylethanone (3a): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.01~8.00 (m, 2H), 7.85~7.81 (m, 4H), 7.53~7.43 (m, 9H), 4.16 (d, J=15.3 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.83 (d, J=5.7 Hz), 136.98, 133.61, 132.17 (d, J=2.7 Hz), 131.99 (d, J=103.3 Hz), 131.13 (d, J=9.8 Hz), 129.26, 128.64 (d, J=12.4 Hz), 128.54, 43.34 (d, J=57.9 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.87; HRMS (ESI) calcd for C₂₀H₁₇NaO₂P [M+Na]⁺: 343.0858, found 343.0862.

  2-(Diphenylphosphoryl)-1-(3-methoxyphenyl)ethanone (3b): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.83~7.78 (m, 4H), 7.59 (d, J=7.7 Hz, 1H), 7.49~7.44 (m, 7H), 7.33~7.29 (m, 1H), 7.09~7.06 (m, 1H), 4.14 (d, J=15.3 Hz, 2H), 3.79 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.64 (d, J=5.7 Hz), 159.68, 138.34, 132.14 (d, J=2.8 Hz), 132.05 (d, J=103.3 Hz), 131.12 (d, J=9.8 Hz), 129.55, 128.62 (d, J=12.3 Hz), 122.20, 120.51, 112.78, 55.42, 43.41 (d, J=58.2 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 27.02; HRMS (ESI) calcd for C₂₁H₂₀NaO₃P [M+Na]⁺: 373.0964, found 373.0967.

  2-(Diphenylphosphoryl)-1-(4-methoxyphenyl)ethan-1-one (3c): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.01~7.99 (m, 2H), 7.85~7.80 (m, 4H), 7.53~7.45 (m, 6H), 6.91~6.89 (m, 2H), 4.11 (d, J=15.3 Hz, 2H), 3.86 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.04 (d, J=5.5 Hz), 163.97, 132.11 (d, J=2.9 Hz), 132.05 (d, J=103.1 Hz), 131.78, 131.13 (d, J=9.8 Hz), 130.14, 128.60 (d, J=12.3 Hz), 113.72, 55.51, 43.17 (d, J=58.0 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 27.15; HRMS (ESI) calcd for C₂₁H₂₀NaO₃P [M+Na]⁺: 373.0964, found 373.0967.

  2-(Diphenylphosphoryl)-1-(o-tolyl)ethan-1-one    (3d): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.89~7.78 (m, 5H), 7.53~7.46 (m, 6H), 7.37~7.33 (m, 1H), 7.29~7.25 (m, 1H), 7.23~7.15 (m, 1H), 4.15 (d, J=15.1 Hz, 2H), 2.32 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 195.68 (d, J=5.6 Hz), 138.96, 137.45, 132.16 (d, J=103.1 Hz), 132.09 (d, J=2.8 Hz), 131.95, 131.83, 131.10 (d, J=9.8 Hz), 130.31, 128.62 (d, J=12.3 Hz), 125.78, 45.64 (d, J=58.7 Hz), 21.27; ³¹P NMR (162 MHz, CDCl₃) δ: 27.31; HRMS (ESI) calcd for C₂₁H₁₉NaO₂P [M+Na]⁺: 357.1015, found 357.1019.

  2-(Diphenylphosphoryl)-1-(m-tolyl)ethan-1-one    (3e): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.83~7.78 (m, 5H), 7.73 (s, 1H), 7.52~7.42 (m, 6H), 7.33~7.26 (m, 2H), 4.14 (d, J=15.3 Hz, 2H), 2.34 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.99 (d, J=5.5 Hz), 138.28, 137.03, 134.41, 132.13 (d, J=2.8 Hz), 132.08 (d, J=103.2 Hz), 131.14 (d, J=9.8 Hz), 129.56, 128.61 (d, J=12.3 Hz), 128.45, 126.59, 43.21 (d, J=58.8 Hz), 21.30; ³¹P NMR (162 MHz, CDCl₃) δ: 26.98; HRMS (ESI) calcd for C₂₁H₁₉NaO₂P [M+Na]⁺: 357.1015, found 357.1019.

  2-(Diphenylphosphoryl)-1-(p-tolyl)ethan-1-one    (3f): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.90~7.79 (m, 6H), 7.51~7.43 (m, 6H), 7.21~7.17 (m, 2H), 4.35 (d, J=15.3 Hz, 2H), 2.34 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.32 (d, J=4.8 Hz), 144.55, 134.58, 132.15 (d, J=2.7 Hz), 132.12 (d, J=101.5 Hz), 131.11 (d, J=9.7 Hz), 129.40, 129.22, 128.59 (d, J=12.3 Hz), 43.13 (d, J=58.4 Hz), 21.69; ³¹P NMR (162 MHz, CDCl₃) δ: 27.01; HRMS (ESI) calcd for C₂₁H₁₉NaO₂P [M+Na]⁺: 357.1015, found 357.1019.

  2-(Diphenylphosphoryl)-1-(2-fluorophenyl)ethan-1-one (3g): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.80~7.76 (m, 4H), 7.73~7.69 (m, 1H), 7.53~7.49 (m, 2H), 7.47~7.42 (m, 5H), 7.16~7.12 (m, 1H), 7.05~7.00 (m, 1H), 4.25 (d, J=14.7 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 190.83 (dd, J=6.0, 2.9 Hz), 161.61 (d, J=254.7 Hz), 135.15 (d, J=9.4 Hz), 132.16 (d, J=103.3 Hz), 132.12 (d, J=2.8 Hz), 131.08 (d, J=9.8 Hz), 130.95 (d, J=1.7 Hz), 128.61 (d, J=12.3 Hz), 126.11 (d, J=11.1 Hz), 124.49 (d, J=3.4 Hz), 116.60 (d, J=23.7 Hz), 46.70 (dd, J=59.3, 7.0 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.75; HRMS (ESI) calcd for C₂₀H₁₆FNaO₂P [M+Na]⁺: 361.0764, found 361.0769.

  2-(Diphenylphosphoryl)-1-(3-fluorophenyl)ethan-1-one (3h): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.83~7.78 (m, 5H), 7.66~7.63 (m, 1H), 7.54~7.43 (m, 6H), 7.42~7.38 (m, 1H), 7.26~7.21 (m, 1H), 4.13 (d, J=15.2 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.69 (dd, J=5.7, 2.3 Hz), 162.65 (d, J=248.0 Hz), 139.03 (d, J=6.4 Hz), 132.29 (d, J=3.0 Hz), 131.76 (d, J=104.2 Hz), 131.07 (d, J=9.8 Hz), 130.25 (d, J=7.6 Hz), 128.70 (d, J=12.4 Hz), 125.35 (d, J=2.9 Hz), 120.64 (d, J=21.5 Hz), 115.64 (d, J=22.7 Hz), 43.58 (d, J=57.1 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.71; HRMS (ESI) calcd for C₂₀H₁₆FNaO₂P [M+Na]⁺: 361.0764, found 361.0767.

  2-(Diphenylphosphoryl)-1-(4-fluorophenyl)ethan-1-one (3i): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.08~8.04 (m, 2H), 7.84~7.79 (m, 4H), 7.56~7.52 (m, 2H), 7.50~7.46 (m, 4H), 7.10~7.02 (m, 2H), 4.12 (d, J=15.2 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.23 (d, J=5.6 Hz), 166.09 (d, J=256.1 Hz), 133.45 (d, J=2.9 Hz), 132.28 (d, J=2.9 Hz), 132.18 (d, J=9.6 Hz), 131.79 (d, J=102.1 Hz), 131.08 (d, J=9.8 Hz), 128.71 (d, J=12.3 Hz), 115.68 (d, J=22.0 Hz), 43.56 (d, J=56.9 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.74; HRMS (ESI) calcd for C₂₀H₁₆FNaO₂P [M+Na]⁺: 361.0764, found 361.0768.

  1-(3, 5-Dichlorophenyl)-2-(diphenylphosphoryl) ethan-1- one (3j): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.80~7.75 (m, 4H), 7.58~7.54 (m, 2H), 7.52~7.47 (m, 5H), 7.34 (d, J=1.8 Hz, 1H), 7.27~7.24 (m, 1H), 4.22 (d, J=14.6 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 193.73 (d, J=5.7 Hz), 137.90, 137.11, 132.26 (d, J=2.7 Hz), 132.04, 131.67 (d, J=103.3 Hz), 131.24, 130.98 (d, J=9.9 Hz), 130.17, 128.71 (d, J=12.4 Hz), 127.40, 46.75 (d, J=57.0 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.74; HRMS (ESI) calcd for C₂₀H₁₅Cl₂NaO₂P [M+Na]⁺: 411.0079, found 411.0073.

  1-(3-Chlorophenyl)-2-(diphenylphosphoryl)ethan-1-one (3k): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.95~7.92 (m, 2H), 7.84~7.79 (m, 4H), 7.58~7.53 (m, 3H), 7.51~7.47 (m, 4H), 7.39 (t, J=7.8 Hz, 1H), 4.14 (d, J=15.3 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.70 (d, J=5.7 Hz), 138.47, 134.87, 133.49, 132.31 (d, J=2.8 Hz), 131.73 (d, J=103.6 Hz), 131.09 (d, J=9.8 Hz), 129.89, 128.98, 128.71 (d, J=12.4 Hz), 127.67, 43.61 (d, J=56.8 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.61; HRMS (ESI) calcd for C₂₀H₁₆ClNaO₂P [M+Na]⁺: 377.0469, found 377.0472.

  1-(4-Chlorophenyl)-2-(diphenylphosphoryl)ethan-1-one (3l): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.99~7.94 (m, 2H), 7.83~7.77 (m, 4H), 7.53~7.41 (m, 6H), 7.40~7.36 (m, 2H), 4.12 (d, J=15.2 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.65 (d, J=5.7 Hz), 140.17, 135.30, 132.32 (d, J=2.8 Hz), 131.76 (d, J=102.1 Hz), 131.06 (d, J=9.8 Hz), 130.78, 128.85, 128.70 (d, J=12.3 Hz), 43.54 (d, J=56.5 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.66; HRMS (ESI) calcd for C₂₀H₁₆ClNaO₂P [M+Na]⁺: 377.0469, found 377.0473.

  1-(4-Bromophenyl)-2-(diphenylphosphoryl)ethan-1-one (3m): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.91~7.88 (m, 2H), 7.83~7.78 (m, 4H), 7.59~7.54 (m, 4H), 7.49~7.48 (m, 4H), 4.11 (d, J=15.2 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.86 (d, J=5.6 Hz), 135.70, 132.28 (d, J=2.5 Hz), 131.84, 131.76 (d, J=102.0 Hz), 131.06 (d, J=9.8 Hz), 130.86, 129.09, 128.71 (d, J=12.3 Hz), 43.62 (d, J=56.6 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.68; HRMS (ESI) calcd for C₂₀H₁₇BrNaO₂P [M+Na]⁺: 420.9963, found 420.9966.

  2-(Diphenylphosphoryl)-1-(3-(trifluoromethyl) phenyl)ethan-1-one (3n): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.26 (d, J=7.8 Hz, 1H), 8.18 (s, 1H), 7.83~7.77 (m, 5H), 7.60~7.52 (m, 3H), 7.50~7.45 (m, 4H), 4.18 (d, J=15.2 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.75 (d, J=5.7 Hz), 137.42, 132.79, 132.40 (d, J=2.9 Hz), 131.60 (d, J=103.3 Hz), 131.08 (q, J=33.3 Hz), 131.07 (d, J=9.9 Hz), 129.90 (q, J=3.7 Hz), 129.30, 128.76 (d, J=12.4 Hz), 125.77 (q, J=3.8 Hz), 123.58 (q, J=272.6 Hz), 43.59 (d, J=56.4 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.65; HRMS (ESI) calcd for C₂₁H₁₇F₃O₂P [M+H]⁺: 389.0913, found 389.0918.

  Methyl 4-(2-(diphenylphosphoryl)acetyl) benzoate (3o): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.02~7.97 (m, 4H), 7.74~7.71 (m, 6H), 7.49~7.39 (m, 6H), 4.11 (d, J=15.2 Hz, 2H), 3.87 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.44 (d, J=5.7 Hz), 166.05, 139.96, 134.06, 132.25 (d, J=2.8 Hz), 131.59 (d, J=103.6 Hz), 130.99 (d, J=9.9 Hz), 129.62, 129.08, 128.64 (d, J=12.4 Hz), 52.42, 43.64 (d, J=56.9 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.72; HRMS (ESI) calcd for C₂₂H₁₉NaO₄P [M+Na]⁺: 401.0913, found 401.0916.

  4-(2-(Diphenylphosphoryl)acetyl)benzonitrile    (3p): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.16 (d, J=2.9 Hz, 2H), 7.83~7.74 (m, 6H), 7.58~7.49 (m, 6H), 4.16 (d, J=15.1 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.77 (d, J=5.8 Hz), 139.78, 132.48 (d, J=2.9 Hz), 132.35, 131.44 (d, J=103.9 Hz), 131.00 (d, J=9.9 Hz), 129.76, 128.82 (d, J=12.4 Hz), 117.90, 116.72, 44.11 (d, J=55.4 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.62; HRMS (ESI) calcd for C₂₁H₁₆NNaO₂P [M+Na]⁺: 368.0811, found 368.0816.

  2-(Diphenylphosphoryl)-1-(4-nitrophenyl)ethanone (3q): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.28~8.21 (m, 4H), 7.84~7.79 (m, 4H), 7.60~7.49 (m, 6H), 4.20 (d, J=15.0 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.65 (d, J=5.7 Hz), 150.46, 141.24, 132.53 (d, J=2.9 Hz), 131.39 (d, J=103.8 Hz), 131.02 (d, J=9.9 Hz), 130.46, 128.85 (d, J=12.4 Hz), 123.69, 44.30 (d, J=55.2 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.91; HRMS (ESI) calcd for C₂₀H₁₇NO₄P [M+H]⁺: 366.0890, found 366.0893.

  2-(Diphenylphosphoryl)-1-(naphthalen-2-yl)ethan-1-one (3r): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.57 (s, 1H), 7.99~7.95 (m, 2H), 7.88~7.81 (m, 6H), 7.61~7.44 (m, 8H), 4.29 (d, J=15.3 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.68 (d, J=5.5 Hz), 135.73, 134.33, 132.36, 132.19 (d, J=2.8 Hz), 132.00 (d, J=103.3 Hz), 131.95, 131.17 (d, J=9.8 Hz), 129.98, 128.86, 128.66 (d, J=12.3 Hz), 128.36, 127.67, 126.77, 124.14, 43.40 (d, J=58.1 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 27.31; HRMS (ESI) calcd for C₂₄H₂₉NaO₂P [M+Na]⁺: 393.1015, found 393.1019.

  2-(Diphenylphosphoryl)-1-(pyridin-3-yl)ethan-1-one(3s): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 9.14 (s, 1H), 8.81~8.64 (m, 1H), 8.41~8.26 (m, 1H), 7.92~7.69 (m, 4H), 7.53~7.36 (m, 7H), 4.15 (d, J=14.8 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.97 (d, J=5.9 Hz), 153.71, 150.41, 136.69, 132.39 (d, J=1.9 Hz), 132.29, 131.60 (d, J=103.8 Hz), 131.03 (d, J=9.9 Hz), 128.77 (d, J=12.3 Hz), 123.42, 43.73 (d, J=55.7 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 26.62; HRMS (ESI) calcd for C₁₉H₁₆NNaO₂P [M+Na]⁺: 344.0811, found 344.0815.

  1-(Diphenylphosphoryl)propan-2-one (3t): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.72~7.68 (m, 4H), 7.51~7.40 (m, 6H), 3.55 (d, J=14.8 Hz, 2H), 2.26 (s, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 201.06 (d, J=5.1 Hz), 132.39 (d, J=2.9 Hz), 131.39 (d, J=102.0 Hz), 130.93 (d, J=9.9 Hz), 128.89 (d, J=12.3 Hz), 48.33 (d, J=56.3 Hz), 32.77; ³¹P NMR (162 MHz, CDCl₃) δ: 26.31; HRMS (ESI) calcd for C₁₅H₁₅NaO₂P [M+Na]⁺: 281.0702, found 281.0705.

  Methyl 2-(diphenylphosphoryl)-2-hydroxy-propanoate (3t')^[11k]: Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.69~7.61 (m, 4H), 7.47~7.35 (m, 6H), 5.34 (s, 1H), 3.21 (s, 3H), 2.89 (dd, J=15.0, 8.2 Hz, 1H), 2.67 (dd, J=15.0, 11.2 Hz, 1H), 1.45 (d, J=2.0 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃) δ: 174.82 (d, J=4.3 Hz), 133.45 (d, J=100.7 Hz), 132.00 (d, J=2.8 Hz), 132.02 (d, J=2.8 Hz), 131.92 (d, J=99.4 Hz), 130.86 (d, J=9.7 Hz), 130.24 (d, J=9.7 Hz), 128.69 (d, J=12.0 Hz), 128.59 (d, J=12.0 Hz), 73.54 (d, J=5.7 Hz), 52.10, 38.69 (d, J=69.4 Hz), 28.74 (d, J=11.5 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 31.24.

  1-(Diphenylphosphoryl)-4-hydroxybutan-2-one (3u): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.83~7.72 (m, 4H), 7.63~7.56 (m, 2H), 7.55~7.48 (m, 4H), 3.87 (t, J=5.3 Hz, 2H), 3.69 (d, J=14.6 Hz, 2H), 2.91 (t, J=5.4 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 203.61 (d, J=5.7 Hz), 132.48 (d, J=2.9 Hz), 131.52 (d, J=103.9 Hz), 130.88 (d, J=9.9 Hz), 128.87 (d, J=12.4 Hz), 57.92, 48.09, 47.04 (d, J=56.3 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 27.94; HRMS (ESI) calcd for C₁₆H₁₇NaO₃P [M+Na]⁺: 311.0808, found 311.0814.

  2-(Di-p-tolylphosphoryl)-1-phenylethan-1-one (3v): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.02~8.00 (m, 2H), 7.73~7.66 (m, 4H), 7.56~7.53 (m, 1H), 7.44~7.41 (m, 2H), 7.28~7.26 (m, 4H), 4.12 (d, J=15.3 Hz, 2H), 2.39 (s, 6H); ¹³C NMR (101 MHz, CDCl₃) δ: 193.05 (d, J=5.6 Hz), 142.62 (d, J=2.9 Hz), 137.07, 133.49, 131.12 (d, J=10.1 Hz), 129.35 (d, J=11.9 Hz), 129.29, 128.83 (d, J=105.9 Hz), 128.49, 43.58 (d, J=57.7 Hz), 21.60; ³¹P NMR (162 MHz, CDCl₃) δ: 27.28; HRMS (ESI) calcd for C₂₂H₂₁NaO₂P [M+Na]⁺: 371.1171, found 371.1168.

  2-(Bis(4-methoxyphenyl)phosphoryl)-1-phenyl-ethan-1- one (3w): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.01~8.00 (m, 2H), 7.75~7.70 (m, 4H), 7.57~7.53 (m, 1H), 7.45~7.42 (m, 2H), 6.98~6.96 (m, 4H), 4.11 (d, J=15.6 Hz, 2H), 3.85 (s, 6H); ¹³C NMR (101 MHz, CDCl₃) δ: 193.25 (d, J=5.5 Hz), 162.55 (d, J=2.9 Hz), 137.08, 133.49, 133.02 (d, J=11.3 Hz), 129.28, 128.50, 123.37 (d, J=110.3 Hz), 114.15 (d, J=13.4 Hz), 55.34, 43.91 (d, J=58.0 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 27.07; HRMS (ESI) calcd for C₂₂H₂₁NaO₄P [M+Na]⁺: 403.1070, found 403.1069.

  2-(Bis(4-fluorophenyl)phosphoryl)-1-phenylethan-1-one (3x): White solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.96~7.94 (m, 2H), 7.83~7.77 (m, 4H), 7.56~7.52 (m, 1H), 7.43~7.39 (m, 2H), 7.17~7.12 (m, 2.2 Hz, 4H), 4.14 (d, J=15.6 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ: 192.70 (d, J=5.6 Hz), 165.19 (dd, J=254.3, 3.2 Hz), 136.77, 133.86, 133.71 (dd, J=11.4, 8.9 Hz), 129.17, 128.64, 127.69 (dd, J=106.9, 3.3 Hz), 116.14 (dd, J=21.5, 13.6 Hz), 43.26 (d, J=59.7 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 25.89; HRMS (ESI) calcd for C₂₀H₁₅F₂NaO₂P [M+Na]⁺: 379.0670, found 379.0673.

  Diethyl (2-oxo-2-phenylethyl)phosphonate (3y): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 8.06 (d, J=7.4 Hz, 2H), 7.64 (t, J=7.4 Hz, 1H), 7.52 (t, J=7.7 Hz, 2H), 4.22~4.14 (m, 4H), 3.68 (d, J=22.7 Hz, 2H), 1.32 (t, J=7.1 Hz, 6H); ¹³C NMR (101 MHz, CDCl₃) δ: 191.98 (d, J=6.7 Hz), 136.49 (d, J=2.1 Hz), 133.69, 129.04, 128.61, 62.68 (d, J=6.5 Hz), 38.44 (d, J=130.1 Hz), 16.24 (d, J=6.4 Hz); ³¹P NMR (162 MHz, CDCl₃) δ: 19.97.

  Supporting Information  Optimization tables; Typical experimental procedures; ¹H NMR, ¹³C NMR and ³¹P NMR spectra for products 3a~3y. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn/.

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• 

  Scheme 1  Phosphorylation of 2-substituted acrylates

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Control experiments

  下载: 全尺寸图片 幻灯片
  

  Scheme 3  Tentative reaction mechanism

  下载: 全尺寸图片 幻灯片

  Table 1.  Optimization of reaction conditions^a

  Entry	Catal.	Cocatal.	Additive	Yieldb/%
  1	CuBr2	-	Et3N	19c
  2	CuBr2	-	Et3N	21d
  3	CuBr2	-	-	22
  4	CuBr2	-	HCl (aq., 1 mol/L)	49
  5	CuBr2	-	HCOOH	29
  6	CuBr2	-	CH3COOH	27
  7	CuBr2	-	PhCH2COOH	24
  8	CuBr2	-	Salicylic acid	22
  9	CuBr2	-	PhB(OH)2	31
  10	CuBr2	-	TsOH	21
  11	CuCl2	-	HCl (aq., 1 mol/L)	45
  12	CuBr	-	HCl (aq., 1 mol/L)	42
  13	Cu(OTf)2	-	HCl (aq., 1 mol/L)	34
  14	Cu(acac)2	-	HCl (aq., 1 mol/L)	38
  15	CuBr2	AgCl	HCl (aq., 1 mol/L)	39
  16	CuBr2	PdCl2	HCl (aq., 1 mol/L)	40
  17	CuBr2	AuCl3	HCl (aq., 1 mol/L)	42
  18	CuBr2	FeBr3	HCl (aq., 1 mol/L)	74
  19	CuBr2	FeCl3	HCl (aq., 1 mol/L)	77
  20	CuBr2	FeCl2	HCl (aq., 1 mol/L)	51
  21	-	FeCl3	HCl (aq., 1 mol/L)	54

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  Table 2.  Screening of substrate scope^a, ^b

  a Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), CuBr2 (5 mol%), FeCl3 (10 mol%), HCl (aq., 0.15 mmol, 1 mol/L), DMF (2.0 mL), O2 (balloon), 40 ℃, 3 h. b Isolated yields based on 1. c Phenethyl 2-phenylacrylate instead of ethyl 2-phenylacrylate. d The hydroxyphosphorylation product 3t' was obtained in 36% yield. e Reaction conditions: Et3N (0.5 mmol) instead of HCl (aq., 0.15 mmol, 1 mol/L).

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