Stereocontrolled synthesis of calyculin A: construction of the C(15)–C(25) spiroketal unit

Abstract
Two concise enantioselective syntheses of the C(15)–C(25) spiroketal unit of calyculin A, using derivatives of allyldiisopinocampheylborane efficieintly to control 1,2- and 1,3-diol stereochemistries, are reported.