Beilstein J. Org. Chem.2015,11, 302–312, doi:10.3762/bjoc.11.35
, Universitetskaya nab. 7–9, 199034 St. Petersburg, Russia 10.3762/bjoc.11.35 Abstract Strained azirinium ylides derived from 2H-azirines and α-diazoketones under Rh(II)-catalysis can undergo either irreversible ring opening across the N–C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or
ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4-oxazines.
Keywords: 2-azabuta-1,3-dienes; azirines; diazo compounds; nitrogen ylides; 2H-1,4-oxazines
5-acyl-substituted 2H-1,4-oxazines. They could, in principle, be prepared from azirines and α-diazo ketones or 2-diazo-1,3-diketones via ring opening across the N–C2 bond in the intermediate azirinium ylides to form 2-azabuta-1,3-dienes and subsequent cyclization of the latter into 2H-1,4-oxazines
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Graphical Abstract
Scheme 1:
Rh(II)-catalyzed synthesis of photochromic 2H-1,4-oxazines from 2H-azirines and α-diazo-β-ketoester...