Intramolecular Ene and Related Reactions, Part 9. Photochemically Induced Synthesis of Allylsilane Carbaldehydes

All articles of this category Allylsilane carbaldehydes are valuable substrates for the tandem Knoevenagel allylsilane and iminium cyclization. They can easily be prepared by a photochemical α-cleavage of cyclic ketones bearing a trimethylsilylmethyl group in the α-position (Norrish Type I cleavage). The photolytic process is facilitated by the silicon due to its stabilization of a radical in the β-position. Irradiation of the ketones 15a-d leads mainly to the aldehydes 16a-d . In addition irradiation of 19a gives mostly the aldehyde 20 .