Reaction of in-situ generated alpha-silylated allylic phosphonate carbanions with aldehydes. An unexpected cyclization reaction

Lithiated alpha-trimethylsilyl cinnamyl-, prenyl- and crotyl-phosphonate carbanions 4 were generated quantitatively in situ from corresponding phosphonates 1, and their reactions with aldehydes were studied. When reacted at 0 degrees C with aromatic or aliphatic aldehydes, the cinnamyl derivative 4a gave phosphonodienes 7 in high yield and with high stereoselectivity. In contrast, the prenyl derivative 4b showed strict gamma-regioselectivity in its reactions with aromatic aldehydes, leading to cyclic organophosphorus compounds 11; with aliphatic aldehydes, a mixture of corresponding heterocyclic compound 11 as major product, and of phosphonodiene 9, as minor product, was obtained. Reactions of crotyl derivative 4c with aromatic or aliphatic aldehydes were highly gamma-regioselective too, and phosphanoalcohols 13 could be isolated upon hydrolysis at -70 degrees C. When warmed near 50 degrees C, alkoxides 12 underwent cyclization reaction to give heterocyclic compounds 14.