Photolysis of 1-azidophosphetan oxides: ring expansion to 2-methoxy-1,2-azaphospholidine 2-oxides and ring opening to methyl alk–ylphosphonamidates in methanol

Abstract

Irradiation of 1-azido-2,2,4,4-tetramethylphosphetan 1-oxide (4) in methanol leads by ring expansion to 2-methoxy-3,3,5,5-tetramethyl-1,2-azaphospholidine 2-oxide (17), and by ring opening to methyl (1,1,3-trimethylbut-3-enyl)phosphonamidate (20). The 2,2,3,3-tetramethyl analogue (5) behaved similarly, except that two isomeric ring expansion products (21) and (23) were obtained, in relative yields indicative of the absence of any marked preference for migration of the primary or tertiary ring-carbon atom. In the case of 1-azido-2,2,3,4,4-pentamethylphosphetan 1-oxide [(6), single geometrical isomer], the product (25) of ring expansion was formed as a mixture of geometrical isomers having the methoxy-group cis or trans to the 4-methyl group. The possible involvement of nitrene and metaphosphonimidate intermediates in these reactions is briefly discussed.