The highly enantioselective Diels–Alderreaction of acetylenic dienophiles is shown to be effectively catalyzed by cationic chiral palladium complexes. Not only the degree but also the sense of enantioselectivity critically depends on the steric demand of ligands. Computational analyses indicate that the steric demand does not affect the endo/exo‐selectivity but the enantioface selectivity of dienes
One-Pot Multistep Bohlmann−Rahtz Heteroannulation Reactions: Synthesis of Dimethyl Sulfomycinamate
作者:Mark C. Bagley、Krishna Chapaneri、James W. Dale、Xin Xiong、Justin Bower
DOI:10.1021/jo048106q
日期:2005.2.1
The synthesis of dimethyl sulfomycinamate, the acidic methanolysis product of the sulfomycin family of thiopeptide antibiotics, from methyl 2-oxo-4-(trimethylsilyl)but-3-ynoate is achieved in a 2,3,6-trisubstituted pyridine synthesis that proceeds with total regiocontrol in 13 steps by the Bohlmann-Rahtz heteroannulation of a 1-(oxazol-4-yl)enamine or in 12 steps and 9% yield by three-component cyclocondensation with N-[3-oxo-3-(oxazol-4-yl)propanoyl]serine and ammonia in ethanol.
Silver-catalyzed synthesis of disubstituted isoxazoles by cyclization of alkynyl oxime ethers
A facile and practical synthesis of 3,5-disubstituted isoxazoles via a silver-catalyzed cyclization and subsequent protonation of alkynyl oxime ethers has been developed. The methodology was successfully applied to the synthesis of a biologically active isoxazolecarboxylic acid. (C) 2011 Elsevier Ltd. All rights reserved.