Racemization mechanisms of alpha-chiral organolithiums: a computational study

ORGN 26

Paul R. Carlier and Yiqun Zhang. Department of Chemistry, Virginia Tech, Blacksburg, VA 24061
Enantiomerically pure organolithium reagents that are chiral at the lithium-bearing carbon would be valuable nucleophiles. However, many organolithium reagents lack configurational stability, as illustrated by Walborsky’s studies of chiral cyclopropylnitrile 1a and isonitrile 1b (below). We have studied the deprotonation of these species by LiNH2 at the B3LYP/6-31+G* level, and have characterized an intramolecular “conducted tour” racemization mechanism for the lithiated products (ammonia complexes). The activation barriers of these processes agree well with Walborsky’s observations that the lithiated isonitrile, but not the nitrile, is configurationally stable.

 

Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry and High Energy Species
8:00 AM-12:00 PM, Sunday, September 7, 2003 Sheraton New York -- Royal Ballroom A, Oral

Division of Organic Chemistry
The 226th ACS National Meeting, New York, NY, September 7-11, 2003