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
(2ca –2ch ) 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