Lithiated α-trimethylsilyl cinnamyl-, prenyl- and crotyl-phosphonate carbanions 4 were generated quantitatively in situfrom 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