The Willgerodt-Kindler reaction was studied on three different model c
ompounds (4-bromo benzaldehyde, 4-fluorobenzaldehyde, 4-methoxyacetoph
enone) with particular emphasis on the influence of the solvent on the
yield of the reaction, Best conditions involved the use of polar apro
tic solvents such as DMF. This finding was applied to the Willgerodt-K
indler 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.