SYNTHESIS, REACTIONS, AND PROPERTIES OF SOME HIGHLY HINDERED DIPHENYL ETHERS

Publisher Website
Google Scholar
Abstract
In the Hems synthesis of diphenyl ethers, an ortho-carbonyl offered less obstruction when held in a lactone ring than when present as an ester. Side reactions interfered with the Hems synthesis of highly hindered diphenyl ethers, and the highly hindered, highly activated ethers produced in the synthesis were easily cleaved by nucleophilic reagents, often in a few minutes at room temperature. The latter fact added a lively interest to the transformation of the ethers into other derivatives. Three of these were of special interest: (a) methyl 2-(6′-amino-4′-carbomethoxy-2′-nitrophenoxy)benzoate (VIc) which existed in remarkably stable dimorphic forms, (b) the dibenzoxazepine VIII, and (c) the quadruply orthosubstituted, asymmetrical 7-(4′-carbomethoxy -6′-laevo-menthoxyacetamino- 2′-nitrophenoxy)metameconine (IX). Attempts to isolate diastereoisomeric substances having the diphenyl ether link as an element of asymmetry failed, the classical explanation of the low configurational stability (due to bending and twisting of bonds) being superior to the quantum mechanical explanation of a tunnelling oscillation of oxygen.This paper describes the synthesis of diphenyl ethers bearing three or four groups ortho to the ethereal linkage, their conversion into asymmetrical derivatives, and our tentative conclusion that the unsymmetrical derivatives cannot be resolved into optical isomers at room temperature. The most interesting part of the paper describes the synthetic methods that must be used in the face of the very great ease of disruption of the ethereal linkage.

This publication has 8 references indexed in Scilit: