Synthetic studies related to diketopyrrolopyrrole (DPP) pigments. Part 2: The use of esters in place of nitriles in standard DPP syntheses: Claisen-type acylations and furopyrrole intermediates

Ethyl 2-aryl-4,5-dihydro-5-oxopyrrole-3-carboxylates react with esters or acyl halides in the presence of a strong base to give 4-acyl derivatives, which exist predominantly as either E- or Z-enols. These are cyclised, either in solution at temperatures > 200degreesC or by microwave irradiation, to 3,6-di substituted 1H-furo[3,4-c]pyrrolediones which, after N-protection, are convertible by reaction with primary amines into novel NN'-disubstituted DPP derivatives. (C) 2004 Elsevier Ltd. All rights reserved.