Asymmetric synthesis of (+)- and (-)-dihydropinidines: diastereoselective addition to chiral imine or 1,3-oxazolidine derived from (R)-phenylglycinolas a single starting material with organometallic reagents

The asymmetric synthesis of the enantiomeric pair of (+)- and (-)-dihydropi nidines has been accomplished. Our strategy was based on the enantioselecti ve construction of both enantiomers of the natural products by using a sing le chiral source, (R)-phenylglycinol. Both routes were carried out by simil ar processes, except for either the presence of an imine or 1,3-oxazolidine intermediate. Excellent diastereoselectivity was observed in the reaction of chiral imines and 1,3-oxazolidines with organometallic reagents, to give the chiral amines in high chemical yields. The absolute configuration of b oth amines was determined by converting each of them into dihydropinidine. The asymmetric synthesis of the (+)- and (-)-dihydropinidine piperidine alk aloids was realized in four steps each and in 46 and 59% overall yield, res pectively, from 6 and 11.