Diastereoselective cycloadditions of nitroalkenes as an approach to the assembly of bicyclic nitrogen heterocycles

A three-component coupling for the rapid assembly of nitrogenated bicycles has been developed that employs the sequential cycloaddition of nitroalkene s as 4 pi components and both an electron-rich vinyl ether and electron-wit hdrawing alkenes. Given the distinct electronic character of nitroalkenes a nd the intermediate nitronates, the coupling represents an atom-economy str ategy without side products resulting from competitive reactions. Either wi th a racemic nitroalkene or an enantiopure nitroalkenyl sugar, these proces ses were regiospecific leading to the formation of bicyclic nitrosoacetals with high facial diastereoselectivity. The stereochemistry of the cycloaddu cts was assigned by NMR spectroscopic techniques, and those of 2 and 15 wer e corroborated by X-ray crystallographic analysis. The unmasking of the nit rosoacetal moiety under mild conditions represents a homologation route for higher aldehydo sugars.