Diastereoselective Formation of a New Palladacycle and Organic Compounds Derived from Vinylcarbenoids as Side Products in the Synthesis of 5-Pallada-<i>trans</i>-tricyclo[4.1.0.0^2,4]heptanes from Acceptor-Substituted Cyclopropenes

Abstract

When a large excess of dimethyl 3,3-dimethylcyclopropene-1,2-dicarboxylate was used in a reaction with Pd2(dba)3·CHCl3, only reduced yields of tetramethyl 3,3,7,7-tetramethyl-5-pallada-trans-tricyclo[4.1.0.02,4]heptane-1,2,4,6-tetracarboxylate were obtained. One side product was the new palladacyle dimethyl 3-(3,4-bis(methoxycarbonyl)-5,5-dimethyl-5H-furan-2-ylidene)-1,1,4,4-tetramethyl-6-oxodihydro-5-oxa-2-palladacyclopropa[c]pentalene 1a,3a-dicarboxylate; its structure was proven by a crystal structure analysis of the bpy complex. The other side products are the 1,3,5-triene methyl (Z)-2-isopropylidene-3,4,5-tris(methoxycarbonyl)-6-methylhepta-3,5-dienecarboxylate (14), the allyl alcohol dimethyl (Z)-2-(1-hydroxy-1-methylethyl)but-2-enedicarboxylate (15), the 1,3-diene dimethyl (Z)-2-isopropenylbut-2-enedicarboxylate (16), and the allyl ether dimethyl 2-isopropylidene-3-methoxysuccinate (17). The formation of most of these side products is interpreted as the reaction of a vinyl carbenoid species with O-nucleophiles