Synthesis of enantioenriched indene-derived bicyclic alcohols and tricyclic cyclopropanes via (−)-sparteine-mediated lithiation of a racemic precursor and kinetic resolution during the cyclocarbolithiation

By treatment of the racemic 3-(indenyl)alkyl carbamate rac-8 with sec-BuLi–(−)-sparteine, cyclocarbolithiation occurs, which is accompanied by kinetic resolution during the cyclisation step. After addition of electrophiles, the stereohomogeneous optically active benzobicyclo[3.3.0]octenols of type 13 are obtained. Increasing the temperature from −78 to −40°C or the application of TMEDA instead of (−)-sparteine yields the formation of the tricyclic cyclopropane 14.