Synlett 2020; 31(09): 878-882
DOI: 10.1055/s-0040-1707968
letter
© Georg Thieme Verlag Stuttgart · New York

Green H2O-Promoted Solvent-Free Synthesis of Enaminocarbonyl Compounds with High Stereoselectivity from Electron-Deficient Terminal Alkynes

Xiao Yun Chen
,
Luming Zhang
,
Yaonan Tang
,
Shuxia Yuan
,
Baocheng Zhu
,
Guang Chen
,
Xiaofang Cheng
We are grateful to the National Natural Science Foundation of China (No. 21602085 and 51902140) and Natural Science Foundation of Jiangsu Province (No. BK20160551) for financial support.
Further Information

Publication History

Received: 27 August 2019

Accepted after revision: 12 February 2020

Publication Date:
03 March 2020 (online)


Abstract

A green H2O-promoted solvent-free hydroamination of electron-deficient terminal alkynes with amines has been developed. All secondary amines, including aliphatic and aromatic amines, gave the corresponding (E)-enamines in good to excellent yields, whereas primary aromatic amines afforded Z-configured products in moderate yields. Propiolates, propyn-1-ones, propynamides, and 1-(ethynylsulfonyl)-4-methylbenzene were explored in this Michael addition.

Supporting Information

 
  • References and Notes

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  • 10 When D2O was used as additive in the reaction instead of H2O, the 1H NMR spectrum of the product (Figure S3; Supporting Information) showed that about half the double-bond protons were replaced by deuterium. However, as hydrogen exchange between both substrates and D2O was found to occur, the degree of participation of H2O/D2O in protonation/deuteration could not be conclusively demonstrated by this experiment.
  • 11 Ethyl (2E)-3-[Methyl(phenyl)amino]acrylate (3a); Typical Procedure Ethyl propiolate (0.5 mmol) was slowly added with stirring to a mixture of N-methylaniline (0.6 mmol) and distilled H2O (0.1 mL) in a 2 mL vial, and the vial then sealed. The mixture was heated at 80 °C with stirring for 1 h. The reaction was then quenched with sat. brine (0.5 mL), and the mixture was cooled to r.t. and extracted with EtOAc (3 × 1 mL) by pipette in the same vial. The combined organic layers were dried (Na2SO4), filtered, and concentrated under reduced pressure. The residue was purified by column chromatography [silica gel, PE–EtOAc (8:1)] to give a pale yellow oil; yield: 96.7 mg (94%). 1H NMR (400 MHz, CDCl3): δ = 7.94 (d, J = 13.2 Hz, 1 H), 7.38–7.31 (m, 2 H), 7.15–7.08 (m, 3 H), 4.94 (d, J = 13.2 Hz, 1 H), 4.18 (q, J = 7.1 Hz, 2 H), 3.24 (s, 3 H), 1.28 (t, J = 7.1 Hz, 3 H). 13C NMR (101 MHz, CDCl3): δ = 169.3, 148.6, 146.7, 129.6, 124.3, 120.0, 90.5, 59.44, 36.7, 14.7. MS (ESI): m/z [M + H]+ calcd for ­C12H16NO2: 206.1; found: 206.1.