No abstract

Coumarins, 4-hydroxycoumarins, and 4-hydroxyquinolin-2(1H)-ones can be conveniently prepared by treatment of alpha-halocarboxylic acid esters of salicylaldehyde, o-hydroxyacetophenone, methyl salicylate, and methyl N-methyl- or N-phenylanthranilates with sodium or lithium telluride. Phenylketene formation competes with cyclization of the alpha-chlorophenylacetate ester of methyl salicylate as demonstrated by a trapping experiment with benzylamine. Elemental tellurium may be recovered and reused.

No abstract

No abstract

A systematic study of the transition metal/base-catalyzed aldol reactions of methyl isocyanoacetate with a wide range of prochiral ketones, giving rise to the 4-(methoxycarbonyl)-5,5-disubstituted-2-oxazolines, has been made. The diastereoselectivity of these reactions was found to be influenced by a mix of several factors, including steric characteristic of the substituents, nature of the catalyst, electrostatic, and electron donor−acceptor type interactions. The former factor, a stereochemical discrimination between the substituents at the ketone carbon, was shown to be the most pronounced in controlling of the stereochemical outcome, which could be markedly improved with a proper choice of the catalyst. In particular, for the reactions of methyl isocyanoacetate with polyhaloalkyl aryl(alkyl) ketones, high diastereoselectivity (80−98% de) was achieved, thus allowing for straightforward and generalized access to the corresponding (2R*,3R*)-β,β-disubstituted-β-hydroxy-α-amino carboxylic acid.