Abstract
Reaction of Oxazolium salts (IX) with dialkyl acylphosphonates (IV) in the presence of triethylamine afforded 1, 4-oxazin-3-one (XII) and/or azetidin-2-one derivatives (XIII). In the reaction of IXa-b with IVa, stable reaction intermediates (Xa-b) were isolated. Some of the products were confirmed to be identical with authentic samples synthesized by an independent pathway. The mechanism of this novel reaction involving ring expansion and ring contraction, substituent effects on the reactivity, and stereochemistry of XIII are discussed.
