Enantioselective Intramolecular [2 + 2 + 2] Cycloaddition of Enediynes for the Synthesis of Chiral Cyclohexa-1,3-dienes

The enantioselective intramolecular [2 + 2 + 2] cycloaddition of various enediynes, where two acetylenic
moieties are connected by a trans-olefinic moiety, gave chiral tricyclic cyclohexa-1,3-dienes using Rh-H8-BINAP catalyst. In the case of carbon-atom-tethered enediynes, enantioselectivity was generally good-to-high regardless of the substituents on their alkyne termini. In contrast, with heteroatom-tethered
enediynes, appropriate substituents were required to induce the oxidative coupling of alkyne and alkene
moieties before that of two alkyne moieties, which would be important for highly enantioselective
intramolecular cycloaddition.