Facile Synthesis of Bicyclo
Orthoesters and Bicyclo Amide Acetals Using α,α-Difluoroalkylamines
作者:Shoji Hara、Seiko Tange、Tsuyoshi Fukuhara
DOI:10.1055/s-0028-1083145
日期:——
triols or diethanolamine using - difluoroalkylamines. The reaction proceeds under milder condi- tions compared with the conventional methods. 4-tert-Butyl-1-(4- ethynylphenyl)trioxabicyclo(2.2.2)octane, a newclass of insecti- cide, was prepared from a triol in 3 steps using a difluoroalkyla- mine.
It is demonstrated for the first time that carboxylic ortho esters may be reduced to acetals using hydrogen as the reducing agent. Hydrogenolysis was performed under mild conditions over commercially available hydrogenation catalysts (5% Pd/C and 5% Pt/C). The present method is especially useful for the selective transformation of carboxylic acids and lactones into acetals.
Oxiranes (epoxides) and oxetanes having a carbonyl functional group are chemoselectively isomerized to different heterocyclic compounds via Lewis acid-promoted 1,6- and 1,7-intramolecular nucleophilic attacks of the carbonyl oxygen on the electron-deficient carbon neighboring the oxonium oxygen: for example, cyclic imides to bicyclic acetals, esters to bicyclic orthoesters, sec-amides to 4,5-dihydrooxazole or 5,6-dihydro-4H-1,3-oxazines, and tert-amides to bicyclic acetals or azetidines. The intramolecular attack of a 1,5-positioned carbonyl oxygen predominantly results in a propagating-end isomerization polymerization. On the other hand, cyclic ethers having a 1,8- or farther positioned carbonyl group undergo conventional ring-opening polymerization. A tetrahydrofuran (oxolane) ring does not open, even with a 1,6-positioned carbonyl group. (C) 2002 Elsevier Science Ltd. All rights reserved.