Synthesis of coumarins, 4-hydroxycoumarins, and 4-hydroxyquinolinones by tellurium-triggered cyclizations.

Coumarins, 4-hydroxycoumarins, and 4-hydroxyquinolin-2(1H)-ones can be conveniently prepared by treatment of α-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 α-chlorophenylacetate ester of methyl salicylate as demonstrated by a trapping experiment with benzylamine. Elemental tellurium may be recovered and reused.