Use of the oxazole-olefin diels-alder reaction in the total synthesis of the monoterpene alkaloids (-)-plectrodorine and (+)-oxerine

A full account of the total synthesis of two monoterpene alkaloids, (-)-plectrodorine [(-)-1] and (+)-oxerine [(+)-3], is presented. The key steps involved are the formation of the oxazole alcohol 10 from the gamma-butyrolactone 9 and the intramolecular Diels-Alder reaction of the oxazole-olefins 13a, b. Since the sign of specific rotation for the synthetic (+)-3 was different from that reported for natural oxerine, the absolute configuration of this alkaloid is not yet fully understood.