Cobalt-Catalyzed Oxidative Phosphonylation of α-Amino Acid

Publication Date (Web): December 12, 2018. Copyright © 2018 American Chemical Society. Cite this:J. Org. Chem. XXXX, XXX, XXX-XXX ...
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Cobalt-Catalyzed Oxidative Phosphonylation of α‑Amino Acid Derivatives and α‑Amino Ketones for α‑Aminophosphonates Zhi-Qiang Zhu,*,†,‡ Li-Jin Xiao,‡ Dong Guo,‡ Xu Chen,‡ Jiu-Jian Ji,‡ Xiao Zhu,‡ Zong-Bo Xie,‡ and Zhang-Gao Le*,†,‡ †

State Key Laboratory of Nuclear Resources and Environment and ‡School of Chemistry, Biology and Material Science, East China University of Technology, Nanchang 330013, P. R. China

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S Supporting Information *

ABSTRACT: A novel and efficient direct oxidative phosphonylation of α-amino ketones and α-amino acid derivatives with dialkyl phosphites by the catalysis of a cobalt salt under air is disclosed. A variety of α-amino ketones and α-amino acid derivatives underwent the reaction well with dialkyl phosphites to produce the desired α-aminophosphonates. This protocol not only provides an alternative synthetic route for the preparation of diverse α-aminophosphonates but also avoids the use of potentially explosive peroxide agents. oxidant.12a In 2016, Li et al. described a novel crossdehydrogenative-coupling (CDC) reaction between glycine amides and H-phosphonates with CuI/TBHP catalysis system.12b Although N-(4- or 2-methoxyphenyl)glycine amides underwent the reaction readily, related α-amino esters could not lead to the desired products at all. In consideration of the biological importance of α-aminophosphonates, and as part of our effort in CDC reactions,13 we herein report a novel cobaltcatalyzed selective phosphonation reaction with α-amino ketones and α-amino acid derivatives for the assembly of αaminophosphonates Importantly, the use of cobalt salt as a practical, cost-efficient catalyst and atmospheric air as an environmentally benign oxidant makes this transformation particularly attractive. In the preliminary studies, we chose N-4-methylphenylglycine ester 1a and diethyl phosphonate 2a as model substrates in the CDC reaction for their optimization investigation. When the model reaction proceeded under the conditions of 10 mol % CuO in acetonitrile (CH3CN) at 80 °C under air, we were pleased to find that the desired α-aminophosphonate 3aa was obtained in 22% yield (entry 1, Table 1). Next, a series of transition-metal salts such as CuCl2, Cu(OTf)2, CoO, CoCl2, Co(OAc)2, and Co(ClO4)2·6H2O were probed (entries 2−7, Table 1), and we found that Co(OAc)2 gave rise to the best yield of 3aa (compare entries 1−6 with entry 7, Table 1; also see the Supporting Information). Control experiment results demonstrated that no desired product 3aa was formed in the absence of a catalyst (entry 8, Table 1). When other oxidants

C−P bond formation reactions have drawn considerable attention due to the prevalence of organophosphorus compounds in pharmaceutical chemicals, phosphine-containing ligands, organic synthesis blocks, and materials science.1 In particular, forging C−P bonds to α-aminophosphonic acids and α-aminophosphonates is considered to be a significantly important conversion because these compounds exhibit many different biological properties such as antitumor,2 antibacterial,3 antifungal,4 catalytic antibody activities,5 and others.6 Typical approaches for their preparations are the Kabachnik− Fields reaction and the Pudovik reaction involving the reaction of dialkylphosphites with imines, which are prepared by the condensation of carbonyl compounds (aldehydes or ketones) and amines.7 Then, a great number of studies by using Lewis acid catalyst and catalyst-free systems have been developed to promote the synthesis of these high-value compounds.8 Despite these achievements, exploring greener and efficient pathways for the preparation of biologically important αaminophosphonate derivatives is still highly desired. Direct phosphorylation of C−H bond is undoubtedly the most straightforward and attractive strategy for the generation of C−P bond.9 In recent years, remarkable works have been conducted on the phosphonylation of C(sp3)−H bonds adjacent to nitrogen with H-phosphonates to produce αaminophosphonates.10−12 However, direct phosphonylation of C(sp3)−H of α-amino acid derivatives with H-phosphonates to provide the corresponding α-aminophosphonates remains rare.12 For example, in 2013, Yang and coworkers revealed a copper-catalyzed oxidative phosphonation reaction of α-amino ketones with diphenylphosphine oxide to give imidoylphosphonates by using tert-butyl hydroperoxide (TBHP) as an © 2018 American Chemical Society

Received: October 18, 2018 Published: December 12, 2018 435

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

Note

The Journal of Organic Chemistry Table 1. Optimization of the Reaction Conditionsa

entry

catalyst

oxidant

solvent

yield (%)b

1 2 3 4 5 6 7 8c 9 10 11 12 13 14d 15e 16e 17e 18e 19e,g 20e,h

CuO CuCl2 Cu(OTf)2 CoO CoCl2 Co(ClO4)2·6H2O Co(OAc)2

air air air air air air air air DTBP TBHP DCP K2S2O8 O2

MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN MeCN DCE toluene MeCN MeCN

22 10 36 8 12 23 38 0 32 33 35 30 37 0 72 83(82)f 52 68 63 80

Co(OAc)2 Co(OAc)2 Co(OAc)2 Co(OAc)2 Co(OAc)2 Co(OAc)2 Co(OAc)2 Co(ClO4)2·6H2O Co(ClO4)2·6H2O Co(ClO4)2·6H2O Co(ClO4)2·6H2O Co(ClO4)2·6H2O

air air air air air air

Reaction conditions: 1a (0.2 mmol), 2a (0.2 mmol), catalyst (10 mol %), solvent (2 mL) at 80 °C under air or oxidant (2 equiv) for 12 h. Isolated yield based on 1a. cIn the absence of a catalyst. dUnder N2 atmosphere. e2a (1.4 mmol). f2a (1.6 mmol). gAt 60 °C. hAt 100 °C.

a

b

proceed at all with those substrates under the standard conditions. Nevertheless, N-arylglycine esters 1f−i bearing a number of different alkyl, such as methyl, isopropyl, tert-butyl, and benzyl groups in the activating ester moiety were found to be suitable coupling partners, giving rise to the corresponding products 3fa−ia in 61−80% yields. Moreover, a range of different dialkyl phosphites 2b−d were also able to react well with N-4-methylphenylglycine ester 1a, delivering the expected products 3ab−ad in 62−95% yields. Unfortunately, no desired product was observed when diphenylphosphine oxide was employed instead of dialkyl phosphites. To evaluate the practicability of this method, N-4-methylphenylglycine ester 1a (6.5 mmol) with diethyl phosphite 2a was performed in gramscale, and the desired α-aminophosphonate 3aa was obtained in 80% yield (1.71 g). For further examining the generality of the present protocol, glycine amides and α-amino carbonyl compounds 1 were also investigated in this CDC reaction with diethyl phosphite 2a. A variety of glycine amides and α-amino ketones 1j−u performed this reaction well with diethyl phosphite 2a to produce the corresponding α-aminophosphonates 3ja−ua in 76−95% yields (Table 3). Glycine amides 1j−l bearing various amino substituents in the amide moiety, such as methylamino, ethylamino, and benzylamino, were good candidates in the present protocol, giving rise to the desired α-aminophosphonates 3ja−la in satisfactory yields. Surprisingly, tertiary amide,= N,N-dimethyl-2-(p-tolylamino)acetamide and simple dipeptide ethyl p-tolylglycylglycinate did not undergo the desired phosphorylation reaction with diethyl phosphite 2a under the standard reaction conditions. Further, a wide range of α-amino ketones 1m−u underwent the reaction well with

were employed, lower or no formation of 3aa was observed (compare entries 9−13 with entry 7, Table 1; also see Supporting Information). The reaction did not occur at all under nitrogen atmosphere; this result attested clearly that air was crucial to this transformation (entry 14, Table 1). The usage amount of diethyl phosphite 2a was also examined, and we found that Co(ClO4)2·6H2O displayed better catalytic efficiency for the yield of 3aa than Co(OAc)2 when 7 equiv diethyl phosphite 2a was employed (compare entry 15 with entry 16, Table 1). Among various solvents screened, MeCN proved to be the most efficient solvent to give 3aa in 83% yield (compare entries 17 and 18 with entry 16, Table 1; also see Supporting Information). Lowering or raising the reaction temperature led to a reduction in the yield of 3aa (compare entries 19 and 20 with entry 16, Table 1). On the basis of the above discussion, it can be concluded that the optimized reaction should proceed under the conditions of 10 mol % of Co(ClO4)2·6H2O in MeCN at 80 °C under air. With optimal reaction conditions in hand, various glycine esters 1 and phosphonates 2 were investigated in the CDC reaction. Different from reported protocol,12b an array of N-arylglycine esters 1a−i performed the reaction readily with diethyl phosphite 2a to provide the corresponding α-aminophosphonates 3aa−ia in 40−90% yields (Table 2). Glycine esters 1a−c wtih electron-rich groups on N-benzene rings reacted more smoothly with diethyl phosphite 2a than did 1d and e with electron-poor groups on N-benzene rings. However, N-2-methylphenylglycine ester with diethyl phosphite 2a afforded a complex mixture of unidentified compounds. In addition, N-methyl, N-Boc, or N-Cbz protected glycine esters were also examined. The reaction did not 436

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

Note

The Journal of Organic Chemistry Table 2. CDC Reaction between N-Arylglycine Esters 1a−i and Dialkyl Phosphites 2a−da,b

Reaction conditions: 1 (0.2 mmol), 2 (1.4 mmol), Co(ClO4)2·6H2O (10 mol %), MeCN (2 mL), at 80 °C under air for 12 h. bIsolated yield based on 1. cProduct 3aa was obtained in 1.71 g. a

diethyl phosphite 2a to generate the expected products 3ma− ua in good to excellent yields. For example, when different functional groups such as methyl and halogen groups were connected on the para-position of amino unit on the Nbenzene ring, the expected products 3na−pa were isolated in high yields. The aryl groups connected with carbonyl groups were also evaluated, and both electron-rich and electrondeficient substituents on the benzene rings in α-amino ketones 1qa−ua led to the corresponding products 3qa−ua in good yields. To investigate the mechanism of this transformation, some control experiments were carried out, and the experimental results are depicted in Scheme 1. When the radical inhibitor 2,6-di-tert-butyl-4-methylphenol (BHT) or 2,2,6,6-tetramethyl1-piperidinyloxy (TEMPO) existed, the reaction was suppressed completely (eq 1). This observation implies that the reaction may undergo a radical process. Next, in the absence of diethyl phosphonate 2a, glycine imine 5 was formed in 53% yield by the oxidation of glycine ester 1a under the standard conditions (eq 2). Then, the reaction between glycine imine 5 and diethyl phosphite 2a was examined, and the expected αaminophosphonate 3aa was generated in 88% yield (eq 3). These results revealed that glycine imine 5 was the key intermediate in this cobalt-catalyzed CDC reaction. Based on the above experimental results and previous reports,12,14 a possible mechanism of this conversion is illustrated as follows (Scheme 2). First, Co(II) activates oxygen in the air to generate a Co(III) peroxy radical,10e,14

which may abstract a hydrogen radical of glycine ester 1a to produce radical 4. Subsequently, radical 4 undergoes a single electron transfer (SET) by the high valent Co(III) to give glycine imine 5 and regenerate Co(II).15 Finally, the attack of reactive diethyl phosphonate 2a on the glycine imine 5 provides the desired α-aminophosphonate 3aa. In summary, a convenient and efficient cobalt-catalyzed oxidative phosphonylation of α-amino acid derivatives and αamino carbonyl compounds for the preparation biologically important α-aminophosphonates was developed. Various glycine derivatives and α-amino ketones allowed the reaction to proceed well with diakyl phosphonates to furnish the desired α-aminophosphonates in satisfactory yields. This approach not only provides an excellent step- and atomeconomic synthetic route for the preparation of diverse αaminophosphonates but also uses atmospheric air as an environmentally benign oxidant.

■

EXPERIMENTAL SECTION

General Information. Unless otherwise indicated, all reagents were purchased from commercial distributors and used without further purification. 1H NMR and 13C NMR were recorded at 400 and 100 MHz respectively, using tetramethylsilane as an internal reference. High-resolution mass spectra (HRMS) were measured on a quadrupole time-of-flight (Q-TOF) mass spectrometer instrument with an electrospray ionization (ESI) source. Melting points were uncorrected. Flash column chromatography was performed over silica gel 200−300 mesh. Thin-layer chromatography (TLC) was carried 437

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

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The Journal of Organic Chemistry

Table 3. CDC Reaction between Glycine Amides 1j−l or α-Amino Ketones 1m−u and Diethyl Phosphite 2a by Cobalt Catalysisa,b

Reaction conditions: 1 (0.2 mmol), 2a (1.4 mmol), Co(ClO4)2·6H2O (10 mol %), MeCN (2 mL), at 80 °C under air for 12 h. bIsolated yield based on 1.

a

Scheme 1. Control Experiments

out with silica gel GF254 plates. N-arylglycine derivatives and αamino ketones 1 were prepared according to the previous reported protocols.12,13 General Procedure for the Synthesis of α-Aminophosphonates 3. To a solution of α-amino derivatives or α-amino ketones 1 (0.2 mmol) in MeCN (2 mL) was added diakyl phosphonates 2 (1.4 mmol) and Co(ClO4)2·6H2O (7.3 mg, 0.02 mmol). Then, the reaction mixture was stirred at 80 °C under air for 12 h. After the reaction was completed, the resulting mixture was concentrated under vacuum, and the residue was subjected to column chromatography

(silica gel, 8:1 petroleum ether/ethyl acetate as an eluent) to afford the desired α-aminophosphonates 3. Ethyl 2-(Diethoxyphosphoryl)-2-(p-tolylamino)acetate (3aa).16 Yield 83% (54.6 mg); light yellow solid; mp 75.2−76.4 °C; 1H NMR (400 MHz, CDCl3): δ 7.00 (d, J = 6.4 Hz, 2H), 6.61 (dd, J = 5.4 Hz, J = 1.4 Hz, 2H), 4.47 (d, J = 18.4 Hz, 1H), 4.27−4.17 (m, 6H), 2.24 (s, 3H), 1.36−1.31 (m, 6H), 1.27 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.5 (d, J = 2.4 Hz), 143.8 (d, J = 9.0 Hz), 129.8, 128.8, 114.2, 64.2 (d, J = 4.5 Hz), 63.6 (d, J = 4.7 Hz), 62.2, 438

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

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The Journal of Organic Chemistry

HRMS (ESI) calcd for C14H23NO5P (M + H)+ 316.1308, found 316.1311. Isopropyl 2-(Diethoxyphosphoryl)-2-(p-tolylamino)acetate (3ga). Yield 61% (41.9 mg); light yellow solid; mp 76.0−77.5 °C; 1 H NMR (400 MHz, CDCl3): δ 7.00 (d, J = 6.4 Hz, 2H), 6.60 (d, J = 6.0 Hz, 2H), 5.11−5.07 (m, 1H), 4.44 (d, J = 18.4 Hz, 1H), 4.25− 4.20 (m, 4H), 2.24 (s, 3H), 1.35 (t, J = 5.4 Hz, 3H), 1.32 (t, J = 5.6 Hz, 3H), 1.27 (d, J = 5.2 Hz, 3H), 1.27 (d, J = 4.8 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.0 (d, J = 2.0 Hz), 143.9 (d, J = 9.0 Hz), 129.8, 128.7, 114.3, 70.0, 64.0 (d, J = 6.2 Hz), 63.4 (d, J = 5.7 Hz), 56.9 (d, J = 118.1 Hz), 21.8, 21.6, 20.5, 16.5 (d, J = 4.1 Hz), 16.4 (d, J = 5.2 Hz); HRMS (ESI) calcd for C16H27NO5P (M + H)+ 344.1621, found 344.1619. tert-Butyl 2-(Diethoxyphosphoryl)-2-(p-tolylamino)acetate (3ha). Yield 67% (47.9 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 7.00 (d, J = 6.4 Hz, 2H), 6.61 (d, J = 6.0 Hz, 2H), 4.37 (d, J = 18.0 Hz, 1H), 4.26−4.12 (m, 4H), 2.24 (s, 3H), 1.46 (s, 9H), 1.36 (t, J = 5.8 Hz, 3H), 1.31 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 167.4 (d, J = 1.3 Hz), 144.2 (d, J = 8.2 Hz), 129.8, 128.5, 114.2, 83.1, 63.9 (d, J = 5.9 Hz), 63.3 (d, J = 6.0 Hz), 57.5 (d, J = 119.2 Hz), 27.9, 20.5, 16.5 (d, J = 4.4 Hz), 16.4 (d, J = 5.4 Hz); HRMS (ESI) calcd for C17H29NO5P (M + H)+ 358.1778, found 358.1776. Benzyl 2-(Diethoxyphosphoryl)-2-(p-tolylamino)acetate (3ia). Yield 80% (62.6 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 7.33−7.30 (m, 5H), 6.98 (d, J = 6.8 Hz, 2H), 6.59 (d, J = 6.8 Hz, 2H), 5.24−5.16 (m, 2H), 4.54 (d, J = 18.8 Hz, 1H), 4.23− 4.06 (m, 4H), 2.23 (s, 3H), 1.26 (t, J = 5.6 Hz, 3H), 1.25 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.5 (d, J = 2.5 Hz), 143.8 (d, J = 10.0 Hz), 135.1, 129.9, 128.9, 128.5, 128.4, 114.3, 67.8, 64.3 (d, J = 6.1 Hz), 63.7 (d, J = 5.8 Hz), 62.2, 56.8 (d, J = 118.4 Hz), 20.5, 16.4 (d, J = 4.0 Hz), 16.3 (d, J = 3.9 Hz); HRMS (ESI) calcd for C20H27NO5P (M + H)+ 392.1621, found 392.1621. Ethyl 2-(Dimethoxyphosphoryl)-2-(p-tolylamino)acetate (3ab). Yield 95% (57.2 mg); light yellow solid; mp 69.2−70.1 °C; 1H NMR (400 MHz, CDCl3): δ 7.01 (d, J = 6.4 Hz, 2H), 6.61 (dd, J = 6.8 Hz, 2H), 4.52 (d, J = 19.2 Hz, 1H), 4.30−4.23 (m, 2H), 3.86 (s, 3H), 3.84 (s, 3H), 2.24 (s, 3H), 1.28 (t, J = 6.4 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.3 (d, J = 2.6 Hz), 143.7 (d, J = 9.4 Hz), 129.9, 129.0, 114.3, 62.4, 56.5 (d, J = 119.4 Hz), 54.5 (d, J = 4.6 Hz), 53.9 (d, J = 5.3 Hz), 20.5, 14.1; HRMS (ESI) calcd for C13H19NO5P (M − H)− 300.1006, found 300.1003. Ethyl 2-(Diisopropoxyphosphoryl)-2-(p-tolylamino)acetate (3ac). Yield 76% (54.3 mg); light yellow solid; mp 67.9−68.6 °C; 1 H NMR (400 MHz, CDCl3): δ 6.99 (d, J = 6.4 Hz, 2H), 6.59 (dd, J = 8.8 Hz, J = 2.0 Hz, 2H), 4.85−4.76 (m, 2H), 4.41 (d, J = 19.2 Hz, 1H), 4.22 (q, J = 6.4 Hz, 2H), 2.23 (s, 3H), 1.36 (d, J = 5.2 Hz, 6H), 1.33 (d, J = 5.2 Hz, 3H), 1.30 (d, J = 5.2 Hz, 3H), 1.26 (t, J = 6.4 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.8 (d, J = 1.6 Hz), 144.1 (d, J = 10.6 Hz), 129.8, 128.6, 114.2, 72.9 (d, J = 6.3 Hz), 72.4 (d, J = 5.8 Hz), 61.9, 57.3 (d, J = 119.6 Hz), 24.3 (d, J = 3.3 Hz), 24.0 (d, J = 2.9 Hz), 23.8 (d, J = 4.3 Hz), 23.7 (d, J = 3.5 Hz), 20.5, 14.1; HRMS (ESI) calcd for C17H29NO5P (M + H)+ 358.1778, found 358.1776. Ethyl 2-(Dibutoxyphosphoryl)-2-(p-tolylamino)acetate (3ad). Yield 62% (47.8 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 6.99 (d, J = 6.4 Hz, 2H), 6.60 (dd, J = 8.8 Hz, J = 2.0 Hz, 2H), 4.48 (d, J = 18.8 Hz, 1H), 4.23 (d, J = 6.4 Hz, 2H), 4.19−4.05 (m, 4H), 2.23 (s, 3H), 1.71−1.61 (m, 4H), 1.46−1.28 (m, 4H), 1.26 (t, J = 5.6 Hz, 3H), 0.96−0.89 (m, 6H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.6 (d, J = 1.8 Hz), 143.9 (d, J = 10.1 Hz), 129.8, 128.7, 114.2, 67.7 (d, J = 6.1 Hz), 67.1 (d, J = 5.8 Hz), 65.5 (d, J = 5.1 Hz), 62.1, 56.7 (d, J = 118.7 Hz), 32.5 (d, J = 5.6 Hz), 32.4 (d, J = 5.0 Hz), 20.4, 18.7, 18.6 (d, J = 1.4 Hz), 14.1, 13.5; HRMS (ESI) calcd for C19H31NO5P (M − H)− 384.1945, found 384.1942. Diethyl (2-(Methylamino)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3ja). Yield 95% (59.7 mg); light yellow solid; mp 110.3−110.9 °C; 1H NMR (400 MHz, CDCl3): δ 7.02 (d, J = 6.8 Hz, 2H), 6.94 (brs, 1H), 6.59 (d, J = 6.4 Hz, 2H), 4.72 (d, J = 6.0 Hz, 1H), 4.25−4.14 (m, 5H), 2.82 (d, J = 3.6 Hz, 3H), 2.25 (s, 3H), 1.34

Scheme 2. Plausible Mechanism

56.8 (d, J = 118.0 Hz), 20.5, 16.5 (d, J = 4.8 Hz), 16.4 (d, J = 5.4 Hz), 14.1; HRMS (ESI) calcd for C15H25NO5P (M + H)+ 330.1465, found 330.1467. Ethyl 2-(Diethoxyphosphoryl)-2-((4-methoxyphenyl)amino)acetate (3ba).16 Yield 90% (62.1 mg); yellow oil; 1H NMR (400 MHz, CDCl3): δ 6.78 (d, J = 7.2 Hz, 2H), 6.66 (d, J = 7.2 Hz, 2H), 4.43 (d, J = 18.4 Hz, 1H), 4.27−4.18 (m, 6H), 3.74 (s, 3H), 1.37− 1.31 (m, 6H), 1.27 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.7 (d, J = 1.8 Hz), 153.4, 140.2 (d, J = 10.3 Hz), 115.7, 114.8, 64.1 (d, J = 5.7 Hz), 63.5 (d, J = 6.0 Hz), 62.2, 57.5 (d, J = 118.2 Hz), 55.7, 16.5 (d, J = 4.8 Hz), 16.4 (d, J = 4.7 Hz), 14.1; HRMS (ESI) calcd for C15H23NO6P (M−H)− 344.1269, found 344.1257. Ethyl 2-([1,1′-Biphenyl]-4-ylamino)-2-(diethoxyphosphoryl)acetate (3ca). Yield 65% (50.9 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 7.52 (dd, J = 6.8 Hz, J = 0.8 Hz, 2H), 7.45 (dd, J = 5.2 Hz, J = 1.6 Hz, 2H), 7.39 (t, J = 6.2 Hz, 2H), 7.29−7.26 (m, 1H), 6.76 (dd, J = 5.2 Hz, J = 1.6 Hz, 2H), 4.68 (brs, 1H), 4.56 (d, J = 18.4 Hz, 1H), 4.31−4.18 (m, 6H), 1.36 (t, J = 5.6 Hz, 3H), 1.33 (t, J = 5.6 Hz, 3H), 1.29 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.4 (d, J = 1.6 Hz), 145.6 (d, J = 8.3 Hz), 140.9, 132.4, 128.7, 128.0, 126.5, 114.3, 64.2 (d, J = 4.7 Hz), 63.7 (d, J = 6.1 Hz), 62.4, 56.8 (d, J = 117.3 Hz), 20.5, 16.5 (d, J = 5.3 Hz), 16.4, 14.2; HRMS (ESI) calcd for C20H27NO5P (M + H)+ 392.1621, found 392.1627. Ethyl 2-((4-Chlorophenyl)amino)-2-(diethoxyphosphoryl)acetate (3da).16 Yield 41% (28.6 mg); light yellow solid; mp 80.2−81.5 °C; 1 H NMR (400 MHz, CDCl3): δ 7.15 (dd, J = 9.2 Hz, J = 2.4 Hz, 2H), 6.61 (dd, J = 9.2 Hz, J = 2.4 Hz, 2H), 4.62 (brs, 1H), 4.45 (d, J = 18.0 Hz, 1H), 4.29−4.14 (m, 6H), 1.35 (t, J = 5.8 Hz, 3H), 1.32 (t, J = 5.8 Hz, 3H), 1.28 (t, J = 5.8 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 168.2 (d, J = 1.6 Hz), 144.8 (d, J = 8.6 Hz), 129.2, 124.1, 115.1, 64.1 (d, J = 5.6 Hz), 63.7 (d, J = 5.4 Hz), 62.4, 56.4 (d, J = 118.9 Hz), 16.5 (d, J = 4.9 Hz), 16.4, 14.1; HRMS (ESI) calcd for C14H20ClNO5P (M − H)− 348.0773, found 348.0767. Ethyl 2-((4-Bromophenyl)amino)-2-(diethoxyphosphoryl)acetate (3ea).16 Yield 40% (31.4 mg); light yellow solid; mp 75.2−76.4 °C; 1 H NMR (400 MHz, CDCl3): δ 7.27 (dd, J = 5.8 Hz, J = 1.4 Hz, 2H), 6.56 (dd, J = 5.6 Hz, J = 1.6 Hz, 2H), 4.65−4.62 (m, 1H), 4.44 (dd, J = 18.6 Hz, J = 7.2 Hz, 1H), 4.29−4.14 (m, 6H), 1.38−1.25 (m, 9H); 13 C{1H} NMR (100 MHz, CDCl3): δ 168.1 (d, J = 1.5 Hz), 145.2 (d, J = 9.4 Hz), 132.1, 115.1, 111.3, 64.1 (d, J = 5.2 Hz), 63.7 (d, J = 5.4 Hz), 62.4, 56.8 (d, J = 118.0 Hz), 16.4 (d, J = 5.2 Hz), 16.3 (d, J = 5.0 Hz), 14.1; HRMS (ESI) calcd for C14H20BrNO5P (M − H)− 392.0268, found 392.0258. Methyl 2-(Diethoxyphosphoryl)-2-(p-tolylamino)acetate (3fa). Yield 78% (49.2 mg); light yellow solid; mp 73.5−74.8 °C; 1H NMR (400 MHz, CDCl3): δ 7.00 (d, J = 6.8 Hz, 2H), 6.60 (d, J = 6.8 Hz, 2H), 4.50 (d, J = 18.8 Hz, 1H), 4.27−4.17 (m, 4H), 3.78 (s, 3H), 2.24 (s, 3H), 1.35 (t, J = 5.2 Hz, 3H), 1.32 (t, J = 5.2 Hz, 3H); 13 C{1H} NMR (100 MHz, CDCl3): δ 169.5 (d, J = 2.4 Hz), 143.8 (d, J = 9.6 Hz), 129.9, 128.9, 114.2, 64.1 (d, J = 4.7 Hz), 63.7 (d, J = 5.4 Hz), 56.6 (d, J = 119.0 Hz), 53.0, 20.4, 16.4 (d, J = 6.4 Hz), 16.3; 439

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

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The Journal of Organic Chemistry (t, J = 6.4 Hz, 3H), 1.33 (t, J = 6.4 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 167.6, 144.1 (d, J = 9.3 Hz), 129.9, 129.2, 114.1, 64.2 (d, J = 5.6 Hz), 63.6 (d, J = 5.3 Hz), 58.3 (d, J = 112.8 Hz), 26.5, 20.4, 16.4, 16.3 (d, J = 6.4 Hz); HRMS (ESI) calcd for C14H24N2O4P (M + H)+ 315.1468, found 315.1466. Diethyl (2-(Ethylamino)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3ka). Yield 87% (57.1 mg); light yellow solid; mp 99.7−101.3 °C; 1H NMR (400 MHz, CDCl3): δ 7.01 (d, J = 6.8 Hz, 2H), 6.98 (brs, 1H), 6.59 (d, J = 6.4 Hz, 2H), 4.76 (brs, 1H), 4.25− 4.15 (m, 5H), 3.34−3.27 (m, 2H), 2.24 (s, 3H), 1.34 (t, J = 5.8 Hz, 3H), 1.33 (t, J = 5.6 Hz, 3H), 1.10 (t, J = 5.8 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 166.8, 144.2 (d, J = 8.8 Hz), 129.8, 129.0, 114.1, 64.1 (d, J = 5.5 Hz), 63.6 (d, J = 6.4 Hz), 58.3 (d, J = 112.0 Hz), 34.6, 20.4, 16.4, 16.3 (d, J = 4.2 Hz), 14.6; HRMS (ESI) calcd for C15H24N2O4P (M − H)− 327.1479, found 327.1482. Diethyl (2-(Benzylamino)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3la). Yield 76% (59.3 mg); light yellow solid; mp 92.4−93.6 °C; 1H NMR (400 MHz, CDCl3): δ 7.29−7.29 (m, 6H), 7.01 (d, J = 6.8 Hz, 2H), 6.60 (d, J = 6.8 Hz, 2H), 4.55−4.38 (m, 2H), 4.24−4.12 (m, 5H), 2.26 (s, 3H), 1.31 (t, J = 5.6 Hz, 3H), 1.29 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 167.0, 144.1 (d, J = 8.7 Hz), 137.7, 129.9, 129.2, 128.6, 127.6, 127.4, 114.2, 64.1 (d, J = 5.7 Hz), 63.7 (d, J = 5.6 Hz), 58.4 (d, J = 112.8 Hz), 43.6, 20.4, 16.4 (d, J = 4.6 Hz), 16.3 (d, J = 5.2 Hz); HRMS (ESI) calcd for C20H26N2O4P (M − H)− 389.1636, found 389.1638. Diethyl (2-Oxo-2-phenyl-1-(phenylamino)ethyl)phosphonate (3ma). Yield 91% (63.2 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.06 (dd, J = 6.0 Hz, 2H), 7.61 (t, J = 5.8 Hz, 1H), 7.50 (t, J = 6.2 Hz, 2H), 7.18 (t, J = 6.2 Hz, 2H), 6.79−6.76 (m, 3H), 5.56 (d, J = 17.2 Hz, 1H), 4.17−4.00 (m, 4H), 1.17 (t, J = 5.6 Hz, 3H), 1.14 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.6 (d, J = 2.0 Hz), 146.5 (d, J = 6.3 Hz), 135.5, 134.0, 129.4, 129.1, 128.6, 119.2, 114.3, 64.0 (d, J = 5.7 Hz), 63.7 (d, J = 5.9 Hz), 59.3 (d, J = 118.0 Hz),16.3 (d, J = 4.4 Hz), 16.2 (d, J = 5.4 Hz); HRMS (ESI) calcd for C18H23NO4P (M + H)+ 348.1460, found 348.1460. Diethyl (2-Oxo-2-phenyl-1-(p-tolylamino)ethyl)phosphonate (3na). Yield 93% (67.1 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.05 (d, J = 6.4 Hz, 2H), 7.60 (t, J = 6.0 Hz, 1H), 7.48 (t, J = 6.2 Hz, 2H), 6.98 (d, J = 6.4 Hz, 2H), 6.68 (d, J = 6.8 Hz, 2H), 5.52 (d, J = 17.6 Hz, 1H), 415−3.99 (m, 4H), 2.22 (s, 3H), 1.18 (t, J = 5.6 Hz, 3H), 1.14 (t, J = 5.8 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.9, 144.2 (d, J = 7.4 Hz), 135.6, 133.9, 129.9, 129.8, 129.1, 128.6, 114.6, 64.0 (d, J = 5.6 Hz), 63.7 (d, J = 5.5 Hz), 59.8 (d, J = 117.8 Hz), 20.5, 16.3 (d, J = 4.5 Hz), 16.2 (d, J = 4.9 Hz); HRMS (ESI) calcd for C19H25NO4P (M + H)+ 362.1515, found 362.1514. Diethyl (1-((4-Fluorophenyl)amino)-2-oxo-2-phenylethyl)phosphonate (3oa). Yield 92% (67.2 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.05 (dd, J = 6.4 Hz, J = 0.8 Hz, 2H), 7.63−7.60 (m, 1H), 7.50 (t, J = 6.0 Hz, 2H), 6.88 (t, J = 7.0 Hz, 2H), 6.73−6.70 (m, 2H), 5.48 (d, J = 17.6 Hz, 1H), 4.14−3.99 (m, 4H), 1.17 (t, J = 5.6 Hz, 3H), 1.15 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.6 (d, J = 2.2 Hz), 156.7 (d, J = 188.4 Hz), 142.8 (d, J = 7.2 Hz), 135.5, 134.1, 129.1, 128.6, 115.8 (d, J = 17.3 Hz), 115.5 (d, J = 5.6 Hz), 64.0 (d, J = 5.9 Hz), 63.8 (d, J = 5.9 Hz), 60.0 (d, J = 117.7 Hz), 16.2 (d, J = 5.1 Hz), 16.1 (d, J = 5.5 Hz); HRMS (ESI) calcd for C18H20FNO4P (M − H)− 364.1120, found 364.1117. Diethyl (1-((4-Chlorophenyl)amino)-2-oxo-2-phenylethyl)phosphonate (3pa). Yield 90% (68.6 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.05 (d, J = 5.6 Hz, 2H), 7.62 (t, J = 5.8 Hz, 1H), 7.50 (t, J = 6.2 Hz, 2H), 7.12 (d, J = 6.8 Hz, 2H), 6.69 (d, J = 7.2 Hz, 2H), 5.49 (d, J = 17.6 Hz, 1H), 5.11 (brs, 1H), 4.13−3.99 (m, 4H), 1.16 (t, J = 5.6 Hz, 3H), 1.14 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.2 (d, J = 1.5 Hz), 145.0 (d, J = 6.6 Hz), 135.4, 134.1, 129.2, 129.1, 128.6, 123.8, 115.4, 63.9 (d, J = 5.9 Hz), 63.8 (d, J = 6.1 Hz), 59.3 (d, J = 118.3 Hz), 16.2 (d, J = 5.5 Hz), 16.3 (d, J = 4.0 Hz); HRMS (ESI) calcd for C18H22ClNO4P (M + H)+ 382.0970, found 382.0966. Diethyl (2-Oxo-2-(p-tolyl)-1-(p-tolylamino)ethyl)phosphonate (3qa). Yield 83% (62.3 mg); light yellow solid; mp 123.8−124.9 °C; 1H NMR (400 MHz, CDCl3): δ 7.96 (d, J = 6.8 Hz, 2H), 7.28 (t,

J = 6.4 Hz, 2H), 6.97 (d, J = 6.4 Hz, 2H), 6.67 (d, J = 6.8 Hz, 2H), 5.49 (d, J = 17.6 Hz, 1H), 4.15−4.00 (m, 4H), 2.42 (s, 3H), 2.21 (s, 3H), 1.19 (t, J = 5.6 Hz, 3H), 1.16 (t, J = 6.0 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.2 (d, J = 1.4 Hz), 145.0, 144.3 (d, J = 7.5 Hz), 133.1, 129.8, 129.3, 128.5, 114.5, 63.9 (d, J = 5.5 Hz), 63.7 (d, J = 5.6 Hz), 59.6 (d, J = 117.8 Hz), 21.8, 20.4, 16.3 (d, J = 5.1 Hz), 16.2 (d, J = 4.0 Hz); HRMS (ESI) calcd for C20H27NO4P (M + H)+ 376.1672, found 376.1675. Diethyl (2-(4-Methoxyphenyl)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3ra). Yield 79% (61.8 mg); light yellow solid; mp 77.8−78.2 °C; 1H NMR (400 MHz, CDCl3): δ 8.06 (d, J = 5.6 Hz, J = 1.2 Hz, 2H), 6.98 (t, J = 6.8 Hz, 2H), 6.96 (d, J = 5.6 Hz, J = 1.2 Hz, 2H), 6.67 (d, J = 6.8 Hz, 2H), 5.45 (d, J = 17.2 Hz, 1H), 4.19− 4.02 (m, 4H), 3.88 (s, 3H), 2.22 (s, 3H), 1.20 (t, J = 5.6 Hz, 3H), 1.18 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 192.8 (d, J = 1.7 Hz), 164.2, 144.4 (d, J = 7.5 Hz), 131.6, 129.8, 128.5, 128.4, 114.5, 113.7, 63.9 (d, J = 6.0 Hz), 63.6 (d, J = 6.0 Hz), 59.4 (d, J = 118.4 Hz), 55.6, 20.4, 16.3 (d, J = 5.5 Hz), 16.2 (d, J = 5.1 Hz); HRMS (ESI) calcd for C20H27NO5P (M + H)+ 392.1621, found 392.1625. Diethyl (2-(4-Fluorophenyl)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3sa). Yield 77% (58.4 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.12−8.09 (m, 2H),7.15 (t, J = 6.8 Hz, 2H), 6.98 (d, J = 6.8 Hz, 2H), 6.67 (d, J = 6.8 Hz, 2H), 5.45 (d, J = 17.6 Hz, 1H), 4.16−4.03 (m, 4H), 2.22 (s, 3H), 1.20 (t, J = 5.8 Hz, 3H), 1.17 (t, J = 5.8 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 193.3 (d, J = 1.2 Hz), 166.2 (d, J = 204.4 Hz), 144.2 (d, J = 7.2 Hz), 132.0, 131.9 (d, J = 6.6 Hz), 129.9, 128.7, 115.7 (d, J = 7.1 Hz), 114.5, 64.1 (d, J = 5.7 Hz), 63.8 (d, J = 6.1 Hz), 59.8 (d, J = 117.6 Hz), 20.4, 16.3 (d, J = 3.9 Hz), 16.2 (d, J = 4.7 Hz); HRMS (ESI) calcd for C19H22FNO4P (M + H)+ 378.1276, found 378.1272. Diethyl (2-(4-Chlorophenyl)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3ta). Yield 81% (64.0 mg); light yellow oil; 1H NMR (400 MHz, CDCl3): δ 8.01 (d, J = 6.8 Hz, 2H), 7.46 (d, J = 7.2 Hz, 2H), 6.98 (d, J = 6.8 Hz, 2H), 6.66 (d, J = 6.4 Hz, 2H), 5.45 (d, J = 18.0 Hz, 1H), 4.17−4.04 (m, 4H), 2.22 (s, 3H), 1.21 (t, J = 5.8 Hz, 3H), 1.18 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 193.8 (d, J = 1.1 Hz), 144.0 (d, J = 7.8 Hz), 140.5, 133.9, 130.5, 129.9, 128.9, 128.8, 114.5, 64.1 (d, J = 5.9 Hz), 63.8 (d, J = 5.9 Hz), 59.9 (d, J = 117.2 Hz), 20.4, 16.3 (d, J = 4.9 Hz), 16.2 (d, J = 4.1 Hz); HRMS (ESI) calcd for C19H24ClNO4P (M + H)+ 396.1126, found 396.1120. Diethyl (2-(4-Bromophenyl)-2-oxo-1-(p-tolylamino)ethyl)phosphonate (3ua). Yield 89% (78.2 mg); light yellow solid; mp 103.2−104.6 °C; 1H NMR (400 MHz, CDCl3): δ 7.93 (dd, J = 5.6 Hz, J = 1.6 Hz, 2H), 7.63 (d, J = 6.8 Hz, 2H), 6.98 (d, J = 6.8 Hz, 2H), 6.65 (d, J = 6.8 Hz, 2H), 5.43 (d, J = 17.6 Hz, 1H), 4.17−4.03 (m, 4H), 2.22 (s, 3H), 1.21 (t, J = 5.8 Hz, 3H), 1.18 (t, J = 5.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ 194.1 (d, J = 2.3 Hz), 144.1 (d, J = 7.9 Hz), 134.3, 131.9, 130.6, 129.9, 129.3, 128.8, 114.5,, 64.1 (d, J = 5.5 Hz), 63.8 (d, J = 5.4 Hz), 59.9 (d, J = 117.8 Hz), 20.4, 16.3 (d, J = 4.7 Hz), 16.2 (d, J = 4.7 Hz); HRMS (ESI) calcd for C19H24BrNO4P (M + H)+ 440.0621, found 440.0616.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b02680.

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Optimization of reaction conditions and 1H NMR and 13 C NMR spectra of all products (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Zhi-Qiang Zhu: 0000-0003-4915-9357 440

DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

Note

The Journal of Organic Chemistry Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (Grants 21602027 and 11765002), the Natural Science Foundation of Jiangxi Province (Grant 20171BAB213006), the Foundation of Jiangxi Educational Committee (Grant GJJ170458), the China Postdoctoral Science Foundation (Grant 2018M632595), and the Scientific Research Foundation of East China University of Technology (Grant DHBK2016112) for financial support.

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DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442

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DOI: 10.1021/acs.joc.8b02680 J. Org. Chem. 2019, 84, 435−442