Regioselective Functionalization. 7. Unexpected Preferences for Bridgehead Migration in Schmidt Rearrangement Syntheses of Novel 2,6-Diazabicyclo[3.2.x]alkan-3-ones (x = 1−3)

Regioselective syntheses of 2,6-diazabicyclo[3.2.x]alkan-3-ones (x = 1−3) 34 by insertion of nitrogen next to the bridgehead (BH) of 2-azabicyclo[2.2.x]alkanones 32 with hydroxylamine-O-sulfonic acid are described. The ketones 32 under Schmidt reaction conditions (HN3/H2SO4) afford major amounts of BH migrated lactams 34 but also, when x = 2 or 3, the methylene (M) migrated lactams, 3,6-diazabicycl[3.2.x]alkan-2-ones 37. The present N-insertion reactions favoring BH migration with azabicyclic ketones contrast markedly with reactions of the related carbocycles 1a , b, which give only methylene migrated lactams 2a , b with HN3/H2SO4. Schmidt reactions of 3-anti/syn-methyl- and 3-anti-phenyl-2-azabicyclo[2.2.2]octan-5-ones 17, 20, and 23 (64:36 ± 9, BH:M) follow the reaction pattern of the parent ketone 14, but the 3-syn-phenyl ketone 26 gives major (65%) methylene migration. The results offer insights into the BH vs M migration dichotomy for the Beckmann and Schmidt reactions of bridged bicyclic ketones.