Abstract
This review summarizes research results concerning the reactions of hydrazonoyl halides with heterocyclic thiones reported by us and other research groups from 1991 to mid 2007. It outlines the utility of such reactions in various aspects of heterocyclic chemistry.
Highlights
Hydrazonoyl halides are a class of compounds with the general formula 1 where X represents a chlorine or bromine group
These compounds are the acyl halides of the so-called hydrazonoic acids 2 as the imidoyl chlorides 3 are the chloride derivatives of imidoic acids 4 (Chart 1)
Reactions of nitrilimines with heterocyclic thiones, having the thiol form 6B, start with the formation of the 1,3-adducts to give the respective thiohydrazonate esters 7 as intermediates, whereas reactions of such 1,3-dipoles with true heterocyclic thiones having the thione form 6A proceed via 1,3-dipolar cycloaddition to the C=S double bond to form the spirocycloadducts namely spirothiadiazoles 8 (Scheme 2)
Summary
Hydrazonoyl halides are a class of compounds with the general formula 1 where X represents a chlorine or bromine group. Reactions of hydrazonoyl halides 1 are usually carried out in the presence of a base catalyst The function of the latter is to convert 1 into the respective 1,3- dipoles 5 which are called nitrilimines or nitrilium imides via 1,3-elimination reaction. Reactions of nitrilimines with heterocyclic thiones, having the thiol form 6B, start with the formation of the 1,3-adducts to give the respective thiohydrazonate esters 7 as intermediates, whereas reactions of such 1,3-dipoles with true heterocyclic thiones having the thione form 6A proceed via 1,3-dipolar cycloaddition to the C=S double bond to form the spirocycloadducts namely spirothiadiazoles 8 (Scheme 2) Both types of intermediates 7 and 8 usually undergo further in situ reactions according to their structures and the reaction conditions leading to either formation of new annelated heterocycles, spiro heterocycles, heterocyclic ring transformation or functional group modification as outlined
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