The synthesis of nor- and bisnorlupanes

Abstract

In the course of our studies on geochemical biomarkers we required a series of lupane standards. We report here an efficient synthesis of lupane (1) in three steps from betulin (3) in an overall yield of 47.2%. 17β(H)-28-Norlupane (2) was obtained in 90% purity employing Barton's method for the decarboxylation of 3-oxolupan-28-oic acid (10). 24,28-Bisnorlupane (4) and 24-norlupane (5) were obtained by a series of reactions involving formation of the oxime, the seconitrile, the epoxynitrile, ring closure, and finally a Wolff–Kishner reduction of the C3 carbonyl to the methylene. Also, to aid in the quantitative determination of these lupanes from oil shales and geological samples, 3-deuterolupane (6) and 2,3-dideuterolupane (7) were needed, and a method for their preparation is reported. Key words: lupane, 24-norlupane, 28-norlupane, 24,28-bisnorlupane, 3-deuterolupane, 2,3-dideuterolupane.