Synthesis of 1,1-Disubstituted Tetrahydroisoquinolines by Lithiation and Substitution, with in Situ IR Spectroscopy and Configurational Stability Studies

Lithiation of N-Boc-1-phenyltetrahydroisoquinolines was optimized by in situ IR spectroscopy. The kinetics for rotation of the carbamate group and for the enantiomerization of the organolithium were determined. The organolithium is configurationally stable at low temperature, and the asymmetric synthesis of 1,1-disubstituted tetrahydroisoquinolines can be achieved with high yields and high enantiomer ratios. The chemistry was applied to the preparation of FR115427 and provides a way to recycle the undesired enantiomer in the synthesis of solifenacin.