Sequential radical cyclization of beta-functionalized allyl bromomethyldimethylsilyl ethers. Application to the regio- and stereo-specific synthesis of an isoprostanoid precursor

The behaviour of allyl bromomethyldimethylsilyl ethers beta-substituted by various radical trapping functions (aldehyde, nitrile or acetylenic) is stu died in tandem radical cyclizations. Only homopropargylic ethers (but-3-yny lic ethers) lead to the formation of cyclic compounds via a 5-exo-trig, 5-e xo-dig or 5-exo-trig, 6-endo-dig mode. The influence of the TMS group locat ed on the acetylenic moiety is shown to be determinant for the regio- and s tereo-specific C5 ring closure (5-exo-dig mode).