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Stab
le si
ly
l viny
lketenes were prepared via the therma
l reaction of Fischer carbene comp
lexes withtriisopropy
lsi
ly
l- or
tert-buty
ldimethy
lsi
ly
l-substituted a
lkynes. The abi
lity of these si
ly
l viny
lketenes toparticipate with carbenoid reagents in [4 + 1] annu
lation reactions was investigated. The best resu
ltswere obtained with diazomethane and substituted diazomethane reagents, which provided cyc
lopentenoneproducts in exce
llent yie
lds and essentia
lly comp
lete stereose
lectivity.