Methyl sorbate reduction

Michael additions to acceptor-substituted dienes are often followed by (spontaneous or induced) cyclizations. This was already noted by Vorlander and Groebel4 who obtained a substituted 1,3-cyclohexanedione by treatment of 6-phenyl-3,5-hexadien-2-one with diethyl malonate (equation 5). Obviously, the 1,4-addition product which is formed initially then undergoes cyclization, ester hydrolysis and decarboxylation. Similarly, reaction of methyl sorbate with methyl 4-nitrobutyrate gave the 1,6-adduct which was reductively cyclized to 6-methyl-l-azabicyclo[5.3.0]decane18 (equation 6). 

The most extensively studied model reaction was the methyl sorbate (CXXIV), trans, tra s-2,4-hexadienoate reduction into methyl 3-hexenoate (CXXV). This substrate represents a suitable simple model for diene fatty... 

Chromium. The complexes Cr(arene)(CO)s are highly selective catalysts for the hydrogenation of dienes to monoenes. A recent study concentrated on the reduction of methyl hexa-2,4-dienoate (sorbate), and the mechanism was found to be similar to that for reaction with iron-carbonyl catalysts. It does not involve rate-determining loss of the arene to give Cr(CO>3 as the active species, as suggested earlier for a different catalytic system, but rather the arene becoming bi- or uni- rather than ter-dentate, so that the diene can be co-ordinated ... 

---