(Trialkylstannyl)copper(I) reagents: preparation and reaction with α,β-unsaturated carbonyl systems. Preparation of β-trialkylstannyl α,β-unsaturated ketones

Abstract

Reaction of Me3SnLi with 1 equivalent of CuBr•Me2S, PhSCu, Me2(MeO)C—C≡C—Cu, or CuCN in tetrahydrofuran (THF) affords the (trimethylstannyl)copper(I) reagents Me3SnCu•Me2S (1) and [Me3SnCuY]Li (Y = PhS (2), Me2(MeO)C—C≡C (4), CN (5)), respectively. Similarly, treatment of a THF solution of Me3SnLi with 0.5 equivalent of CuBr•Me2S provides (Me3Sn)2CuLi (3), while reaction of n-Bu3SnLi with PhSCu (1 equivalent) gives [n-Bu3SnCuSPh]Li (6). Reagents 2 and 6 readily transfer (in a conjugate sense) the R3Sn group to conjugated enones (e.g. 7–9) and structurally simple enoates (e.g. 10), but do not react with β,β-disubstituted α,β-unsaturated esters (e.g. 11–13). Reaction of reagent 2 with the enone 26 under "normal" conditions produces, in addition to the expected ketone 28, a significant amount of the double conjugate addition product 30. A similar result is obtained with ethyl propenoate (27). However, reaction of 26 and 27 with reagent 2 in the presence of acetic acid provides cleanly and efficiently the "simple" conjugate addition products 28 and 29, respectively. Reagent 1 does not react, or reacts very sluggishly, with α,β-unsaturated carbonyl compounds. β-Trialkylstannyl α,β-unsaturated ketones (e.g. 37–46) can be produced smoothly and efficiently by reaction of the corresponding β-iodo enones (e.g. 32–36) with reagents 2 (or 1) and 6.