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.
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