Imines and derivatives. Part 22. Photoisomerization of the N,N′-dioxides of N,N′-dialkyl-2,2,4,4-tetramethylcyclobutane-1,3-di-imines
Photoisomerization of the N,N′-dioxides of two N,N′-dialkyl-2,2,4,4-tetramethylcyclobutane-1,3-di-imines occurs in a stepwise manner via the analogous mono-oxaziridine-mononitrone, dioxaziridine (and/or monoamide-mononitrone), and monoamide-mono-oxaziridine intermediates en route to the diamide products. The relative configurations of all products have been deduced by n.m.r. methods (chemical shift non-equivalence and n.O.e.d. spectroscopy). The stereochemistry of the photoisomerization reactions can be rationalized in terms of steric and stereoelectronic effects.