D/H Exchange in Nitro Diastereomers

Recent Studies on the Regioselective C-Protonation of Enol Derivatives using Carbonyl-Containing Proton Donors

Enolate protonation can occur by two different pathways. With strong acids regioselective protonation generally occurs on the oxygen of the enolate to give an enol and then acid catalysed tautomerisation leads directly to the thermody-namically preferred carbonyl motif. However, with much weaker acids kinetic protonation on carbon can occur to give directly the carbonyl derivative. This review discuss recent developments into the use of chelating acids to promote this stereochemically important C-protonation and we comment on factors that appear to promote this selectivity.

Efficient and Convenient Heterogeneous Palladium-Catalyzed Regioselective Deuteration at the Benzylic Position

The Pd/C-catalyzed efficient and regioselective hydrogen-deuterium (H-D) exchange reaction on the benzylic site proceeded in D2O in the presence of a small amount of H2 gas. The use of the Pd/C-ethylenediamine complex [Pd/C(en)] as a catalyst instead of Pd/C led to the efficient deuterium incorporation into the benzylic site of O-benzyl protective groups without hydrogenolysis. These H-D exchange reactions provide a post synthetic and D(2)-gas-free deuterium-labeling method on a wide variety of benzylic sites using D2O as the deuterium source and heterogeneous Pd/C or Pd/C(en) as a reusable heterogeneous palladium catalyst under mild and neutral conditions.

Efficient H/D Exchange Reactions of Alkyl-Substituted Benzene Derivatives by Means of the Pd/C–H2–D2O System

A method for efficient and extensive H/D exchange of substituted benzene derivatives which is catalyzed by heterogeneous Pd/C in D(2)O as a deuterium source under hydrogen atmosphere is described. Multi-deuterium incorporation into unactivated linear or branched alkyl chains that bear a carboxyl, hydroxyl, ether, ester, or amide moiety and are connected with a benzene ring was achieved by using the Pd/C-H(2)-D(2)O system. The present method does not require expensive deuterium gas or any special equipment.