a Reaction conditions: 1aa (0.3 mmol), divinylzinc (0.33 mmol), catalyst (3 mol %), THF (2.5 mL), rt, 10 h. Determined by 1H NMR using 1,3,5-trimethoxybenzene as an internal standard. The data in parentheses is the isolated yield. The iron catalysts used in this study are all preprepared. ND = Not detected. b 30% 4,4’-((1E ,3E )-2,4-dimethylhexa-1,3,5-triene-1,3-diyl)bis(methoxybenzene) was isolated.
Subsequently, we investigated the effect of alkyl moieties of the aryl-alkyl acetylenes (Scheme 2). The reactions with the alkynes having primary alkyl groups, a benzyl group, and secondary alkyl groups all afforded the corresponding cis -addition products (2ca2ch ) in good to excellent yields (85–99%), indicating that the catalytic system was not sensitive to properties of the alkyl moiety of the alkyne substrates.
Scheme 2 Iron-catalyzed vinylzincation of aryl-alkyl acetylenes