Enantiomerically Pure Lactones. 3. Synthesis of and Stereospecific Conjugate Additions to α,β-Unsaturated Lactones

Article abstract of DOI:10.1021/jo01309a009

A general synthetic approach to both enantiomers of α,β-unsaturated lactones of general formula 1 has been devised, the first synthesis of the naturally occuring antipode of massoilactone (1b) exemplifying the approach.Interestingly, the specific rotation of massoilactone (and its enantiomer) is higher than that of the natural material isolated from formicine ants.A key step in the sequence involves chromatographic separation of rationally selected diastereomeric derivatives of racemic intermediates. Compounding the utility of an approach to optically active, type 1 lactones is the observation that conjugate additions of organometallic reagents to such lactones proceed with a high degree of stereospecificity, affording lactones of general formula 2. The conformational behavior of lactone 1a is considered as is the solvation of δ-lactones by fluoroalcoholic chiral solvating agents such as 2,2,2-trifluoro-1-(9-anthryl)ethanol (8).