Titanium tetrachloride-mediated aza Diels–Aldercycloaddition using a chiral diene and an aza dienophile proceeds in highly diastereoselective manner to form a dehydropiperazic acid derivative in high yield, and diastereoselectivity of the reaction depends on the quantity of titanium tetrachloride.
The highly efficient synthesis of (R)- and (S)-piperazic acids, components of naturally occurring antibiotic cyclodepsipeptides, was achieved in 80% overall yield by the use of a proline-catalyzed asymmetric alpha-hydrazination as the key step. (C) 2004 Elsevier Ltd. All rights reserved.