Preparation of polycyclic systems by sequential 5-exo-digonal radical cyclization, 1,5-hydrogen transfer from silicon, and 5-endo-trigonal cyclization

Radicals of type 1 undergo 5-exo diagonal cyclization, and the resulting vi nyl radical abstracts hydrogen from silicon to afford a silicon-centered ra dical. This radical closes in a Ei-endo trigonal manner to generate radical s of type 4, which are reduced (4 --> 5) by stannane, except when the start ing acetylene carries a terminal trimethylstannyl group. In this case, radi cals 4 expel trimethylstannyl radical to afford vinyl silanes 6. The stereo chemical outcome of the radical cascade 1 --> 5 is controlled by the stereo chemistry of the oxygen-bearing carbon in 1 (see starred atom). The sequenc e can be initiated by carbon-, alpha -substituted carbon-, oxyacyl-, and ca rbamoyl radicals and generates a silicon-containing ring fused onto a carbo cycle or heterocycle. Numerous examples are described, as well as a number of transformations of the final cyclization products, especially their resp onse to n-Bu4NF and to BF3. OEt2, reagents that cleave the newly formed car bon-silicon bond.