Desymmetrization of 4-dimethylsiloxy-1,6-heptadiynes through sequential double silylformylation.

[reaction in text] Desymmetrization of dimethylsilyloxyalkadiynes (1) by Rh-catalyzed intramolecular silylformylation affords 5-exo-(formylmethylene)oxasilacyclopentanes 2 in high yields. Novel sequential double silylformylation of 1a also provides desymmetrization, giving 3-(3-silyl-2-formylprop-2-enyl)-5-exo-(formylmethylene)oxasilacyclopentanes 4 in excellent yields. Reduction of 2a and 4 with NaBH(4) gives the corresponding 5-exo-(hydroxymethylmethylene)oxasilacyclopentanes 3a and 5, respectively.