Preparation of Chiral Bisoxazolines: Observations on the Effect of Substituents
作者:Scott E. Denmark、Noriyuki Nakajima、Olivier J.-C. Nicaise、Anne-Marie Faucher、James P. Edwards
DOI:10.1021/jo00120a036
日期:1995.7
A series of enantiomerically pure 4-substituted bisoxazolines 1a-f, 2c, and 2e was prepared from naturally derived or synthetic amino alcohols and malonyl dichloride derivatives. The formation of the bisoxazolines was accomplished in two stages: (1) preparation of the bis-amides of the malonyl derivatives with the amino alcohols and (2) cyclization of the hydroxy amides 4 by either of two general protocols; (1) heating with thionyl chloride in toluene or (2) formation of the bismesylate and then heating with aqueous or alcoholic base. The latter procedure was found to be more reliable especially for bisoxazolines with bulky substitutents at C(4). The C(4) trityl-substituted hydroxy amide 4f produced the bis(acylaziridine) 10 by cyclization on the nitrogen atom using KOH/MeOH, but afforded the desired bisoxazoline If by the action of SOCl2/Et(3)N. The synthesis of the nonnaturally derived amino alcohols using the Evans asymmetric azidation procedure is also described.
Enantioselective Cyclopropanation of Allylic Alcohols. The Effect of Zinc Iodide
作者:Scott E. Denmark、Stephen P. O'Connor
DOI:10.1021/jo9702397
日期:1997.5.1
catalytic, enantioselective cyclopropanation of allylicalcohols is examined with bis(iodomethyl)zinc as the reagent and bis-methanesulfonamide 7 as the catalyst. Significant rate enhancement was observed when 1 equiv of zinc iodide was present, but more importantly, the enantiomeric excess of the product cyclopropane increased from 80% to 89% for the substrate cinnamyl alcohol. Reaction studies and spectroscopic