Synthesis of oxa-aza spirobicycles by intramolecular hydrogen abstraction promoted by N-radicals in carbohydrate systems

The preparation of 1-oxa-6-azaspiro[4.4]nonane, 1-oxa-6-azaspiro[4.5]decane, 6-oxa-1-azaspiro[4.5]decane, and 1-oxa-7-azaspiro[5.5]undecane ring systems by 1,6- and 1,7-hydrogen atom transfer promoted by phosphoramidyl radicals in carbohydrate models is described. The N-radicals are generated by reaction of dibenzyl phosphoramidate derivatives of C-glycosides with (diacetoxyiodo)benzene and iodine through an homolytic fragmentation of iodoamide intermediates.