Solvent effect in the Wollgerodt-Kindler reaction

The Willgerodt-Kindler reaction was studied on three different model compounds (4-bromo benzaldehyde, 4-fluorobenzaldehyde, 4-methoxyacetophenone) with particular emphasis on the influence of the solvent on the yield of the reaction, Best conditions involved the use of polar aprotic solvents such as DMF. This finding was applied to the Willgerodt-Kindler reaction of two difficult substrates, i.e. 3-methyl-6-formyl-2(3H)-benzoxazolinone and 3-methyl-6-formyl-2(3H)-benzothiazolinone with various secondary amines.