Modular Synthesis of Heterocyclic Carbene Precursors

Abstract

A series of N-heterocyclic carbene precursors, containing an imidazoline or tetrahydropyrimidine framework, were prepared from omega-chloroalkanoyl chlorides. The sequential attachment of nitrogen nucleophiles and subsequent ring closure gave, depending on the reagents used, either the desired dihydroimidazolium and tetrahydropyrimidinium salts or their parent heterocycles. In this latter case, the second substituent was introduced in an alkylation step. The preparation of carbene precursors bearing chiral or bulky substituents was acieved with comparable efficiency.

Polymer‐Supported, Carbon Dioxide‐Protected N‐Heterocyclic Carbenes: Synthesis and Application in Organo‐ and Organometallic Catalysis

“…Recently, the use of CO 2 adducts of NHCs attracted much attention in organocatalysis as well as in synthesis of the corresponding NHC-metal complexes. [6,7,28] In this article, we describe the synthesis and application of a polymer-supported, CO 2 -protected N-heterocyclic carbene. It was prepared via ring-opening metathesis copolymerization of 1,4,4a,5,8,8a-hexahydro-1,4,5,8-…”

Functionalised Saturated‐Backbone Carbene Ligands: Yttrium and Uranyl Alkoxy–Carbene Complexes and Bicyclic Carbene–Alcohol Adducts

“…[14] A number of synthetic routes to substituted imidazolinium proligands have been developed. These include a modular substituted diamine synthesis with subsequent ring closure, [15] multicomponent synthesis by using a combination of amine, aldehyde, isocyanide and alkyl halide, [16] the intramolecular "hydroamidiniumation" of alkenes, [17] and a template synthesis with an azido isocyanide at a tungsten metal centre. [18] Late metal complexes containing alcohol and phenolfunctionalised saturated NHC ligands have been reported, see Figure 2: Seeking an analogy with salicylaldimine ligands, Grubbs reported the synthesis of o-hydroxyaryl-substituted NHCs and showed that the Pd adducts C were stable.…”

An Efficient Synthesis ofN-Alkyl-N-arylputrescines and Cadaverines

“…Recently, Ramírez et al reported the synthesis of two derivatives, by a three-step strategy starting from ω−haloalkanoyl chlorides, 21 in which the substituted amino group is generated from an amide, while the primary amine results from reduction of an azide. 22 N-Alkylation is conceptually the most straightforward disconnection towards secondary and tertiary amines. 23 Although this transformation seems rather simple, the fact that the newly formed amines are also nucleophilic brings about the formation of bisand/or polyalkylation by-products.…”