P. Desai et al., Reactions of alkyl azides and ketones as mediated by Lewis acids: Schmidt and Mannich reactions using azide precursors, J AM CHEM S, 122(30), 2000, pp. 7226-7232
The Lewis acid-promoted reactions of alkyl azides with ketones can afford s
everal products. Chief among these result from a Schmidt-like insertion of
the azide into the carbon-carbon bond adjacent to the carbonyl group. Alter
natively, an acid-promoted rearrangement of the azide to an iminium species
can occur, mostly with benzylic azides; the iminium species can then be tr
apped by the enol of the carbonyl compound in a variation of the Mannich re
action. The scope of each of these reactions, the dependence of the observe
d products upon azide and ketone structure, and the nature of acid promotio
n are discussed. In broad strokes, cyclohexanones and other cyclic ketones
react in the presence of TiCl4 to afford insertion products, whereas the Ma
nnich route predominates when benzyl azide and triflic acid are used. The f
eatures that lead to each reaction type and possible mechanistic implicatio
ns are discussed.