Stereoselective total synthesis of (+/-)-thielocin Al beta

The stereospecific total synthesis of (+/-)-thielocin A1 beta has been achi eved from the common intermediate ethyl 5-formyl-2,4-dihydroxy-3,6-dimethyl benzoate (8). The racemic synthesis was achieved based on the key reaction of a 4-methyl-3,4-dihydroxy cyclohexadienone 38 with a quinone methide der ived at low temperature from the fluoride ion catalyzed composition of pipe ridinium salt 40. The resulting condensate (31) was homologated by successi ve esterification with protected monomeric phenol 41 to provide, after care ful removal of the protecting groups, the desired thielocin A1 beta.