Formation of five- and six-membered carbocycles with nitrogenated tetrasubstituted carbons by radical addition-carbocyclization of alkynyl ketoxime ethers

C3-Ketoxime ethers bearing alkynes with terminal delta-yne or internal gamma-yne functions were prepared in five or six steps and similar to 20% overall yield from commercial glucofuranose derivatives. Their thiyl-, stannyl-, or carbon radical-promoted addition-carbocyclization gave five- or six-membered carbocycles nitrogenated at one of the bridgehead positions. For internal gamma-yne ethers the tandem process was strongly dependent on both the alkyne substituent and the radical-promoting species and could be directed toward either the five- or the six-membered carbocycle. These results are presented and discussed in the context of studies working toward (-)-tetrodotoxin.