Stephen Challenger

Amination of ethers using chloramine-T hydrate and a copper(I) catalyst

Amination of C-H bonds activated by ether oxygen atoms is facile with chloramine-T as nitrene source and copper(I) chloride in acetonitrile as catalyst. For cyclic ethers the hemiaminal products are generally stable and can be isolated pure. For acyclic ethers, the hemiaminal products, as expected, fragment with elimination of alcohol to yield imines. When activation of benzylic positions is remote through a conjugated system, stable benzylamine derivatives are isolated. Mechanistic studies are consistent with concerted insertion of an electrophilic nitrenoid into the C-H bond in the rate-determining step, though in an asynchronous manner with a more activated substrate.

Stereoselective synthesis of a candoxatril intermediate via asymmetric hydrogenation

Abstract A four step synthesis of a chiral glutarate half ester intermediate, required for the preparation of candoxatril, has been developed from t-butyl acrylate. The key steps in this route include a stereoselective synthesis of a trisubstituted alkene and its asymmetric hydrogenation with a Ru-BINAP catalyst.

THE SYNTHESIS OF GEM-CYCLOPENTYL SUBSTITUTED GLUTARATES VIA THE OXIDATIVE RING CONTRACTION OF 2-ACETYLCYCLOHEXANONES

ABSTRACT A two step synthesis of differentially protected gem-cyclopentyl glutarates has been developed from 2-acetylcyclohexanone and acrylates. The key step involves an oxidative ring contraction reaction with hydrogen peroxide. The methodology has been used to prepare intermediates used in the preparation of the atriopeptidase inhibitor candoxatril.