Silicon-oxygen heterocycles from thermal, photochemical, and transition-metal-catalyzed decomposition of alpha-(alkoxysilyl and alkenyloxysilyl)-alpha-diazoacetates

Photolysis of (ethoxy)silyl-, (propyloxy)silyl-, and (isopropyloxy) silyl-s ubstituted diazoacetates la-e leads to tetrahydro-1,2-oxasiloles 2a-c by in tramolecular C-H insertion of a carbene intermediate. Photochemical or cata lytic decomposition of (allyloxysilyl)diazoacetates 3a-e results in intramo lecular cyclopropanation which provides 3-oxa-2-silabicyclo[3.1.0]hexane sy stems 5a-e. In contrast, the thermal reaction of 3b-d gives rise to 2,5-dih ydro-1,2-oxasiloles 4b-d, which are Likely to be formed on a pyrazoline rat her than a carbene route. For (3-butenyloxysilyl)diazoacetate 3f, all modes of decomposition generate the 3-oxa-2-silabicyclo[4.1.0]heptane system 7. Fluoride-induced cleavage of the bicyclic systems 5b-d provides trans-2-hyd roxyalkyl-1-cyclopropanecarboxylates 9 diastereospecifically.