Modified Synthesis of Heptahelicene and Its Resolution Into Single Enantiomers

Abstract

A practical synthesis of racemic heptahelicene has been develeped being based on key [2+2+2] cycloisomerization of bis[2-(but-3-yn-1-yl)-1-naphthyl]acetylene under CpCo(CO)2/PPh3 or CpCo(C2H4)2 catalysis. The application of the Ni(cod)2 catalyst with (-)-(Sa)-(2'-methoxy-1,1'-binaphthalen-2-yl)diphenylphosphane resulted in enantioselective triyne cyclization to provide (+)-7,8,11,12-tetrahydroheptahelicene in 40% ee. Optically pure (-)-(M)- and optically highly enriched (+)-(P)-heptahelicene were obtained on a milligram scale by resolution of racemate by chiral HPLC on a semipreparative Whelk-O1 column.