Enantioselective Total Synthesis of All of the Known Chiral Cleroindicins (C-F): Clarification Among Optical Rotations and Assignments

Enantioselective syntheses of all of the named chiral members of the cleroindicin family (C-F) are reported. This effort demonstrates the synthetic utility of a 2,4-dihydroxybenzaldehyde as a starting material for natural product synthesis through the use sequential o-quinone methide chemistry and diastereoselective dearomatization. Natural cleroindicin F was shown to be nearly racemic, and an optically pure synthetic sample of cleroindicin F was found to racemize under slightly basic conditions. All other natural chiral cleroindicins are shown to be partially racemic.