Radical cyclization of (bromomethyl)dimethylsilyl propargyl ethers. Regio-, chemo- and stereoselectivity.
摘要:
Radical cyclization of (bromomethyl)dimethylsilyl propargyl ether derivatives 1 is a powerful reaction with a high degree of regio-, chemo-, and stereoselectivity. Trisubstituted olefins 3, cyclopentene derivatives 5, and diquinane system 7j are obtained in good yields by a judicious choice of unsaturated substituents. Triquinane frameworks could be obtained stereoselectively from a suitable acyclic substrate of type 1 in a one-pot reaction. First attempts have not yet allowed us to aim at this goal due to interesting (1,5) hydrogen transfers. Moreover, we have intercepted, for the first time, the alpha-cyclopropyl radical which is involved in the Stork-Beckwith mechanism of the 5-versus 6-membered ring formation in the vinyl radical cyclization.
Radical cyclization of bromomethyldimethylsilyl propargyl ethers—VIII. Bimolecular stereoselective hydrogen abstraction by trisubstituted vinyl radicals. A new example of rare (1,4) hydrogen transfer.
作者:Michel Journet、Max Malacria
DOI:10.1016/s0040-4039(00)74170-0
日期:1992.3
Experiments with Bu3SnD show that trisubstituted vinyl radicals 2 abstract hydrogen bimolecularly from tin hydride. A high degree of stereoselectivity is observed and depends on the nature of the substituents connected to C-1 of bromomethyldimethylsilyl propargyl ether derivatives 1. Radicalcyclization of 5-bromomethyldimethylsiloxy-2,2,5-trimethyl-3-hexyne 1b is totally stereoselective and a very