Sceptrin - Enantioselective Synthesis of a Tetrasubstituted alltrans Cyclobutane Key Intermediate.

The asymmetric synthesis of both enantiomers of tetrasubstituted all-trans dimethyl 3,4-diacetylcyclobutane-1,2-dicarboxylate with high enantiomeric purity (>98 % ee) using a valine-derived chiral auxiliary in a diastereoselective photodimerization is reported. The absolute configuration was assigned by single-crystal X-ray diffraction analysis. Because this cyclobutane is a key intermediate in the total synthesis of (-)-sceptrin and ageliferin, our findings strengthen the recently revised absolute configurations of these pyrrole-imidazole alkaloids. [ABSTRACT FROM AUTHOR]