Synthetic Studies on and Mechanistic Insight into [W(CO)(5)(L)]-Catalyzed Stereoselective Construction of Functionalized Bicyclo[5.3.0]decane Frameworks

Stereoselective preparation of a variety of synthetically useful functionalized bicyclo[5.3.0]decane derivatives was achieved by tandem cyclization of 3-siloxy-1,3,9-triene-7-yne derivatives based on the electrophilic activation of alkynes catalyzed by [-W(CO)(5)(L)]. The reaction proceeded smoothly under photoirradiation, and various substrates were cyclized to give the corresponding bicyclic compounds with up to four chiral centers stereospecifically. Reactions of siloxydienes with a silyl substituent as an equivalent of a hydroxyl group also proceeded with wide generality to afford silyl-substituted bicyclo[5.3.0]decanes, which were highly useful as synthetic intermediates. Stereochemical studies concerning the silyl enol ether moiety suggested that two types of reaction pathway for the formation of seven-membered rings were present. The reaction of (Z)-enol silyl ethers proceeded through Cope rearrangement of cis-di-vinylcyclopropane intermediates, and that of (E)-enol silyl ethers by 1,4-addition of the dienyl tungsten species at the position a to the metal atom. In the reactions of siloxydiene derivatives with silyl substituents, all possible dia-stereomers could be synthesized stereo-selectively by changing the geometry of the silyl enol ether and enyne moieties.