The stereochemistry of the furanoditerpenoids α-, β-, and δ-caesalpin

Abstract

Under the conditions of the Serini reaction the benzofuran (4) derived from α-caesalpin rearranges to the diketone (5) with a cis-A,B ring-junction, while on mild base treatment the benzofuran mesylate (II) from δ-caesalpin undergoes a pinacol-type rearrangement to the hemiacetal (12); consideration of the steric course of these reactions, in conjunction with other evidence, allows the assignment of the relative stereochemistry of α-, β-, and δ-caesalpins as in (1), (2), and (3), respectively.