Radical cyclizations of acylgermane oxime ethers and hydrazones: Direct routes to cyclic hydrazones and oximes

Efficient syntheses of omega-halo-, phenylseleno-, and vinylacylgermane hydrazones and oxime ethers have; been developed, and the radical cyclizations of these substrates have been studied. The preparation of substituted triphenylacylgermanes has been improved through a copper-mediated coupling of acid chlorides and LiGePh3. Condensation of various acylgermanes with O-benzyl hydroxylamine or N,N-dimethylhydrazine efficiently generates the new acceptor systems, which undergo 5-exo cyclizations in good yields. The acylgermane hydrazone and -oxime ether radicals have cyclization rate constants of about 10(7) s(-1) and are thus better accepters than the parent acylgermanes.