Asymmetric synthesis of pent-3-yl ( R)-6-methyl-cyclohex-1-ene carboxylate

Abstract

An expeditious asymmetric synthesis of pent-3-yl ( R)-6-methyl-cyclohex-1-enecarboxylate has been achieved in four steps in 42% overall yield employing as the key step a domino reaction initiated by a highly diastereoselective lithium amide 1,4-conjugate addition to a nona-2,7-diendioic diester followed by a 6- exo- trig cyclisation of the thus formed enolate. Cope elimination protocol of the cyclic adduct affords, depending on the lithium amide used, the corresponding nitro-compound or the expected cyclohexene derivative. The methyl group attached to the cyclohexane ring is achieved by selective ester hydrolysis and subsequent Barton decarboxylation.