237058-22-9Relevant academic research and scientific papers
Thermal and Lewis acid catalyzed diastereoselective intramolecular Diels-Alder reaction on α,β-unsaturated amides derived from (-)-8- aminomenthol
Andres, Celia,Garcia-Valverde, Maria,Nieto, Javier,Pedrosa, Rafael
, p. 5230 - 5236 (2007/10/03)
Stereochemical aspects of the intramolecular Diels-Alder reaction on perhydro-1,3-benzoxazines derived from (-)-8-aminomenthol bearing α,β- unsaturated amides and the dienic component attached at C-2 are described. The thermal cyclization of 2-(2'-furyl) derivatives 2, 6, and 7 exclusively afforded mixtures of exo adducts. The product selectivity was highly dependent on the solvent of the reaction. In CH2Cl2, the kinetic products 3, 8, and 9 always predominated, whereas in hexane or toluene, less polar solvents, the thermodynamic adducts 4, 10, and 11 were formed as major diastereoisomers. In cyclizations catalyzed with equimolar or 2-fold excess of Lewis acid, the kinetic stereiosomers were predominant. Some Lewis acids catalyzed the reaction, but diethylaluminum chloride was the most effective. The cyclization on the perhydro-1,3-benzoxazine 13, bearing an open dienic component, was much less stereoselective, and a mixture of two exo and two endo possible stereoisomers were formed. Elimination of the menthol appendage in two steps by reductive ring opening of the N,O-acetal moiety and oxidation-elimination yielded enantiomerically pure tetrahydroisoindoline derivatives.
