The synthesis of some unsaturated 4-substituted-g-lactones

Thesynthesisof type1 lactone stared fromtheeasilyavailable3prepared in several steps fromdihydroxyacetone.Theprotectionof thehydroxygroupwasperformedunder standard conditions using tert-butyldimethylchlorosilane (TBDMSCl)/NEt3 in DMF as solvent to afford 4 in 90%yield (Scheme 1). For the introduction of the double bond into the lactone C5 position, tert-butoxy bis(dimethylamino)methane (Bredereck’s reagent) was used. This reagent, which is easily made, reacted with the activated methylene group of the lactone 4. Heating Bredereck’s reagent and this lactone at 60 oC without solvent produced 5 in 70%yield. The enaminomoiety in 5was transformed inmoderate yield to the exomethylene double bond by reduction with NaCNBH3 under acidic