Radical cyclisation onto C-3 of 1,6-anhydro-β-D-mannopyranose derivatives. Application to the formation of the C8a centre of (-)-tetrodotoxin

Article abstract of DOI:10.1016/S0040-4039(97)00460-7

Starting from 1,6-anhydro-β-D-mannopyranose, compounds 7a-d, which have a ketoxime ether at C3 and a carbon radical precursor tethered to the hydroxyl group at position 2, were efficiently prepared. While alkyl π-radicals derived from 7a and 7b failed to cyclize, the vinyl σ-radicals derived from 7c and 7d underwent the desired 1,5-exo cyclization, affording advanced precursors of (-)-tetrodotoxin, This type of transformation should be useful for the formation of sterically crowded nitrogen-bearing carbon centers in carbohydrate-derived substrates.