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Abstract
N-(1-Haloalkyl)azinium halides are readily available through a three-component reaction of an azine, an aldehyde, and a thionyl halide. Those salts represent activated forms of the starting aldehydes and can be used advantageously for the preparation of other azinium salts, imines, 1,1diamines, and a wide range of nitrogen (fused) heterocycles. Recently it has also been demonstrated that N-(1-haloalkyl)azinium halides can be transformed into bis(1,3,4-thiadiazolo)1,3,5-triazinium halides, a novel class of versatile tricyclic systems that exhibits many useful synthetic potentialities.
Highlights
The chemistry of N-(1-haloalkyl)heteroarylium salts (1, Figure 1), one of the leading activities of E
The first N-(1-haloalkyl)pyridinium halides (3, Scheme 1) described in the literature were obtained by bromination of phenacyl pyridinium derivatives 2
The mechanism suggested (Scheme 4) to explain the formation of N-(1haloalkyl)heteroarylium halides [1] by the three-component reaction discovered by Anders is based on a 1H-NMR study of the rates of formation of 1. 6c Kinetic data ruled out the presence of a preequilibrium between the aldehyde and the thionyl halide or between the heterocycle and the thionyl halide. It was suggested 6c that the azine could add to the aldehyde to form a betaine prior to interact with the thionyl halide. subsequent O-sulfinylation and elimination of sulfur dioxide would afford the salts
Summary
The chemistry of N-(1-haloalkyl)heteroarylium salts (1, Figure 1), one of the leading activities of E. Anders developed a procedure that has the advantage of a much wider scope of applicability.6 This three-component reaction involves an azine, an aldehyde, and a thionyl halide (Scheme 2) in an inert solvent, generally at room temperature and without any particular experimental precaution. 7 Based on exploratory experiments and a kinetic study 6c of the rate of formation of N-(1-haloalkyl)azinium halides, Merrifield’s resin linked through an ether bound to position 6 of quinoline or position 5 of isoquinoline emerged as highly attractive insoluble auxiliaries. Such solid reagents were readily available by coupling Merrifield’s resin with 6-hydroxyquinoline or 5-hydroxyisoquinoline in a hot mixture of aqueous sodium hydroxide and N,N-dimethylformamide for 6 hours. It was suggested 6c that the azine could add to the aldehyde to form a betaine prior to interact with the thionyl halide. subsequent O-sulfinylation and elimination of sulfur dioxide would afford the salts
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