A short and efficient asymmetric synthesis of (−)-frontalin, (−)-exo-isobrevicomin and a volatile contributor of beer-aroma

The natural products, (−)-frontalin and (+)-exo-isobrevicomin were synthesized employing Sharpless asymmetric epoxidation and ZrCl4-catalyzed intramolecular acetalization as the key steps. (−)-Frontalin was synthesized in three steps with a 61.4% overall yield and 89.9% ee and (−)-exo-isobrevicomin also obtained in an overall satisfactory yield of 10.1% and 97% ee. We have also synthesized the volatile contributor of beer aroma in a 96% ee.