Simple Stereoselective Synthesis of Unsaturated Lactone Intermediates and Their Conversion into Natural Dihydropyranones and Their Enantiomers#

The stereoselective synthesis of the unsaturated lactone intermediates, (S) - and (R)-2-(6-oxo-3, 6-dihydro-2Hpyran- 2-yl) acetaldehydes has been accomplished from propane 1,3 diol employing Maruoka asymmetric allylation and ring closing metathesis reaction. The intermediates were converted into two natural dihydropyranones, 6 (R)-4-oxopent-2- enyl 5,6-dihydro-2H-pyran-2-one and (R)- rugulactone and their enantiomers through Wittig olefination.