Abstract The title compounds 5a-c and 7a-m have been prepared by Vilsmeier formylation of 4-aminocoumarins 1 yielding aldehydes 2, and subsequent condensation of 2 with CH acids in the presence of piperidine. This condensation probably proceeds via the intermediate ylidenemalonic esters 4. By means of detailed 1 H-and 13 C-NMR studies a Dimroth-type rearrangement of intermediates 6f-m has been found to take place in the course of the ...