A Route to 1-Deoxynojirimycin and 1-Deoxymannojirimycin Derivatives with Quaternary Centers Adjacent to the Ring Nitrogen from Methyl α-d-Mannopyranoside

6-Alkylated-8-azido-1,6-octadiene derivatives were prepared from methyl α-d-mannopyranoside. The sequence to allylic azide precursors included a Horner–Wadsworth-Emmons reaction with a concomitant epimerization that ultimately enabled synthesis of 1-deoxynojirimycin as well as 1-deoxymannojirimycin derivatives. Thermally promoted allylic acid rearrangement followed by triazoline formation, then decomposition to aziridine and finally reaction with acetic acid was used to generate products that have quaternary anomeric centers adjacent to the piperidine ring nitrogen atom (cyclic α-tertiary amines). The stereoselectivity is accounted for based on minimization of steric interactions in the transition state structure, favoring the product where the methyl substituent is equatorial and the vinyl group prefers to be axial.