The 1,3,4-Oxadiazole and 1,3,4-Thiadiazole Coupling of Norbornenes and 7-Oxanorbornenes under High Pressure: New Structures, Mechanistic Detail and Synthetic Applications
The synthesis of polarofacial spacer molecules: a new twist in the coupling of ring strained olefins with oxadiazoles.
作者:Ronald N. Warrener、Douglas N. Butler、Wen Yan Liao、Ian G. Pitt、Richard A. Russell
DOI:10.1016/s0040-4039(00)85989-4
日期:1991.4
New approaches to the synthesis of rigid spacer molecules in which an oxygen-bridge bestows the facial polarity is described: attempts to couple 7-oxanorbornenes together using 1,3,4-oxadiazoles yields inverted, non linear products in a stereospecific reaction which differs significantly from that known to obtain with norbornenes.
Reaction of 2,5-bis-trifluoromethyl-1,3,4-oxadiazole with 7-oxanorbornenes revisited: Experimental and quantum-chemical study of reaction stereoselectivity
The stereochemical outcome of reaction of 2,5-bis-trifluoromethyl-1,3,4-oxadiazole with 7-oxanorbornenes under various conditions was investigated. For the first time, microwave irradiation in carrying this type of reactions was used, resulting in comparable yields in significantly shorter reaction times. Regardless on substrate, in all reactions mixtures of the two isomeric O-3-[3]polynorbornanes, bent and linear were obtained, with slight preference for bent structure. In some cases, retro Diels-Alder fragmentation was observed resulting in formation of isobenzofuran species. Reaction mechanism was also studied computationally (RHF/6-31G* method), and the origin of stereoselectivity explained by repulsive lone pair interactions between oxygen bridges in the transition state of the 1,3-dipolar addition. (C) 2009 Elsevier B.V. All rights reserved.