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Stable silyl vinylketenes were prepared via t
he t
hermal reaction of Fisc
her carbene complexes wit
htriisopropylsilyl- or
tert-butyldimet
hylsilyl-substituted alkynes. T
he ability of t
hese silyl vinylketenes toparticipate wit
h carbenoid reagents in [4 + 1] annulation reactions was investigated. T
he best resultswere obtained wit
h diazomet
hane and substituted diazomet
hane reagents, w
hic
h provided cyclopentenoneproducts in excellent yields and essentially complete stereoselectivity.