and tetraflouraboric acid the solvent is then removed in vacuo from the dried magnesium sulfate organic layer and the residue is distilled to provide a mixture of the isomers exo brevicomin and endo brevicomin solvent removal may readily be accomplished by employing a rotary evaporation at about 0 u00b0 c it has been determined experimentally that the resultant mixture will consist of about 55 to 60 endo brevicomin and about 40 to 45 exo brevicomin among the characterizing tests which can be employed to confirm the result are relative retention times of the two isomers on a carbowax 20m glc 1 h nuclear magnetic resonance spectrum of the mixture and the mass spectrum of each isomer obtained by combined gas chromatography mass spectrometry it is found in lieu of use of ether in the workup of the brevicomins other low boiling hydrocarbons such as for example pentane hexane cyclohexane or other suitable organic solvents such as ethyl acetate chloroform and methylene chloride may be employed if desired in preparing the substrate and the reactive metal reducing agent it would generally be preferred to prepare them independently for subsequent admixture however should it be desired they can be prepared simultaneously in the same container with the reduction times being slightly longer in order to provide further guidance regarding the synthesis of the present invention a specific example will now be considered a preferred approach involves the diels alder addition of phenyl vinyl sulfide and methyl vinyl ketone treatment of the adduct with a reducing agent followed by trapping the anion with propionaldehyde the reactive metal reducing.