INTRAMOLACULAR DIELS-ALDER REACTIONS OF SILICON SUBSTITUED DIENES.SYNTHESIS WITH HOMO-ALLYL SILANES.

Article abstract of DOI:10.1016/S0040-4020(01)88588-4

Metallation of 3-vinyl-5-trimethylsilyl-1-pentene (16) with n-BuLi gives a Si substitued pentadienyl anion reagent for bisannelation of ortho-alkenyl benzaldehydes.Tricyclic olefin 23b produced by this method is a homo-allylsilane which undergoes protodesylilation to 4-vinyl-12-methoxy-18,19-bisnor-podocarpa-8,11,13-triene 24b.The addition of β-(trimethylsylil)ethyl magnesium bromide (12) to 12-methoxy-18,19-bisnor-5β-podocarpa-8,11,13-triene-4-one 27 gave the corresponding alcohol 29.When 29 and related γ-hydroxy silanes are treated with acid, dehydratation to allylsilane and protodesilylation to exocyclic vinyl compounds result.Alcohol 29 produces 24b in 93percent yield.Compound 24b can be converted in several steps to podocarpic acid.