6-tert-Butyl-4-methyl-and 6, 8-di-tert-butyl-4-methylcoumarin were prepared from tert- butylphenols and diketene via the corresponding aryl acetoacetates. 6-tert-Butyl-4-methyl- thiocoumarin (6) was obtained from 6-tert-butylthiophenol. Thionation with Lawesson's or davy's reagent led to the related thion-and dithiocoumarins. The structures were proved by nmr spectroscopy and an x-ray structure analysis of 6.