Facile Double Nucleophilic Addition of Thiols and Tetraallyltin to Latent 2-Alkynals Using in situ Hydrolysis of the Imino Functionality Promoted by Tin(IV) Chloride Pentahydrate

Abstract

In the presence of SnCl₄˙5H₂O, a mixture of thiols and tetraallyltin underwent 1,4- and 1,2-addition, respectively, with the imines derived from 3-alkynals to give (Z)-1-sulfenyl-1,5-alkadien-3-ols in good yields, where the hydrolysis of the intermediary imino species was found to be crucial.

Key words

alkynes - conjugate addition - imino compound - Lewis acid - vinyl sulfide

References

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8

A Typical Procedure for the Addition Reaction: To a suspension of SnCl₄˙5H₂O (31.2 mg, 0.06 mmol) in PhCH₃ (1.5 mL) was added a solution of N-(1-phenethyl)phenyl-propargylidenamine (46.7 mg, 0.2 mmol) in CH₂Cl₂ (1.5 mL) at -85 °C, and the mixture was stirred at -85 °C for
5 min. A solution of benzyl mercaptan (37.3 mg, 0.3 mmol) in PhCH₃ (1.5 mL) was added to the resulting mixture at
-85 °C, and the mixture was stirred at -85 °C for 10 min. A solution of tetraallyltin (28.3 mg, 0.1 mmol) in PhCH₃ (1.5 mL) was added to the resulting mixture at -85 °C and the mixture was gradually warmed to r.t. during 17 h. Sat. aq NaHCO₃ was added to the mixture which was extracted with EtOAc. The combined extracts were dried (Na₂SO₄) and concentrated in vacuo to give a crude oil. Purification on silica gel TLC (n-hexane:EtOAc = 4:1 as an eluent) gave (Z)-1-benzylthio-1-phenylhexa-1,5-dien-3-ol (47.6 mg, 84%) as a colorless oil.

9

When TiCl₄ or SnCl₄ was used as a Lewis acid, only 1,4-addition of thiol was observed.

10

The olefin geometry was determined using the NOESY experiment.