Abstract
Irradiation of cis trimethylsilyl aldehyde 9 with UV light generated by a medium-pressure mercury lamp with Pyrex glass filter gave decarbonylated product 11 in 98% yield. Under the same conditions, the corresponding trans trimethylsilyl aldehyde 10 was decarbonylated to afford the same product (11) in 89% yield. The trimethylsilyl group directed the fragmentation of the diyls generated from 9 and 10 by preventing oxa-di-π-methane rearrangement and the 1,3 formyl migration. The results indicated that the alkyl radical intermediates, generated by photolysis, can be stabilized by a trimethylsilyl group at the β position; these β-trimethylsilyl alkyl radicals did not eliminate to give alkenes and trimethylsilyl radicals. By use of the stabilizing effect exerted by silicon, photolysis of cis trimethylsilyl aldehyde 33 gave a 98% yield of isomeric trimethylsilyl alkenes 34-36 in a ratio of 10.9:1.0:1.4. Similarly, photolysis of the corresponding trans trimethylsilyl aldehyde 37 afforded a 83% yield of the same products in a ratio of 1.0:25.5:1.6. Furthermore, cis trimethylsilyl aldehyde 38 was photolyzed to produce a 98% yield of isomeric trimethylsilyl alkenes 39-41 in a ratio of 10.9:1.3:1.0; trans trimethylsilyl aldehyde 42 gave a 99% yield of the same trimethylsilyl alkenes in a ratio of 0.1:32.0:1.0. In all of these decarbonylations, the trimethylsilyl group remained in the reaction products. © 1989 American Chemical Society.