Titanium(IV) Enolates of 2-Nitrocarboxylic Esters and Their Oxidative Chlorination. A Convenient Route to α-Chloro-α-nitrocarboxylates

Abstract

A new method for the synthesis of 2-chloro-2-nitrocarboxylic esters from 2-nitrocarboxylates is described. The procedure consists of the oxidative chlorination of titanium(IV) enolates of 2nitro esters in the presence of ammonium nitrate. Esters of 2-chloro-2-nitrocarboxylic acids are formed in very good to quantitative yields. Application of this method for the chlorination of a,a¢-dinitrodicarboxylates leads to a,a¢-dichloro-a,a¢-dinitrocarboxylic esters with high meso-diastereoselectivity. The absence of ammonium nitrate from the reaction mixture affects the reduction of nitro groups and leads to partial transformation of 2-nitrocarboxylic esters into 2-(hydroxyimino)carboxylates.

Titanium Enolate Chemistry at the Beginning of the 21st Century

“…Unlike the described 2‐isothiocyanatocarboxylates, 2‐nitrocarboxylic acid esters formed very stable titanium(IV) enolates P that did not undergo any dimerization. Addition of ammonium nitrate as an oxidizing agent led to nearly quantitative α‐chlorination to give gem ‐chloronitrocarboxylic acid esters 73 in very high yields 111. The same experiment carried out in the absence of any oxidant yielded a mixture of gem ‐chloronitrocarboxylates and ( E )‐2‐(hydroxyimino)carboxylic acid esters 74 .…”