Diastereoselective dearomative cycloaddition of bicyclobutanes with pyridinium ylides: a modular approach to multisubstituted azabicyclo[3.1.1]heptanes.

Diastereoselective (3+3) cycloaddition between bicyclobutanes and pyridinium ylides forms azabicyclo[3.1.1]heptanes pyridine dearomatization.