Synthese und Photoisomerisierung von sterisch gehinderten 2,6-Dialkylpyridin-N-oxiden Synthesis and Photoisomerization of Sterically Hindered 2,6-Dialkylpyridine-N-oxides

Synthesis o f the new sterically hindered pyrid ine-1-oxides 2c and 6a-c is described. Copper(II)-catalyzed photolysis o f 2 and 6a in aqueous medium provides only small am ounts o f 2-acylpyrroles 8 and 10 a together w ith by-products. Exclusive form ation and better yields of 10 can be received upon irradia tion o f 6 in none protic solvents at low tem perature. In troduc­ tion o f bulky substituents as in 6 failed to stabilize any o f the postulated interm ediates in order to be identified during photoreaction . It is assum ed that the high rate o f polym erization is caused by unstable 1,3-oxazepines like 13.