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

Abstract

Lithiated α-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 °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 γ-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 γ-regioselective too, and phosphonoalcohols 13 could be isolated upon hydrolysis at –70 °C. When warmed near 50 °C, alkoxides 12 underwent cyclization reaction to give heterocyclic compounds 14.