The palladium-catalyzed addition of various vinyl compounds to dimethyl acetylenedicarboxylate

Article abstract of DOI:10.1016/0022-328X(93)83194-Z

The catalyst precursor (E = COOCH3) reacts with simple vinyl compounds and dimethyl acetylenedicarboxylate to give cyclic 1:2-, 2:1- and 2:2-addition products, namely substituted cyclohexadiene or benzene, cyclopentene and cyclooctadiene derivatives, which can be separated by column chromatography.Palladacyclopent-2-enes, palladacyclohepta-2,4-dienes and palladacyclohept-4-enes, which cannot be trapped, are suggested to be intermediates in the reaction.Different types of products are obtained depending on the nature of the vinyl compound: while α-methyl styrene gives only a cyclohexadiene species following 1:2-addition, vinyl ethers along with 1:2-addition undergo 2:1- and even 2:2-addtition, and cyclopentene and 1,5-cyclooctadiene derivatives are formed.In the course of the reaction with vinyl ethers, alcohols are formed, probably in a reductive elimination step from Pd-H-intermediates in which an alkoxy group occupies a β-position and also in palladium-mediated aromatization of initially formed alkoxy cyclohexadiene and bisalkoxy cyclohexene products.Yields and product ratios can be influence by changing the fixed ligand in the catalyst complex.