Benzo-oxadiazoles, synthesis

Oxadiazoles and their benzo derivatives find use in applications as diverse as pharmaceuticals, analytical reagents, propellants and explosives, starting materials in organic synthesis, and for polymer preparation and modification. 

An alternahve method had been reported in the literature [12] to prepare [1,2,4] triazolo[4,3-a]piperazines (Route B, Scheme 5.9) via the condensahon of a chloromethyl oxadiazole with 1,2-phenylenediamine to afford the benzo fused compounds. The reachon condihons reported for this approach were harsh and the yields were low, presumably due to the poor nucleophilicity of 1,2-phenylenedi-amine. However, we felt that the synthesis of 3 could potentially be accomplished under milder reachon condihons because of the enhanced nucleophilicity of... 

A large body of information on the methods of synthesis, application, structure, and properties of all known five-membered nitroazoles - pyrazoles, imidazoles, triazoles, tetrazoles, oxazoles, isoxazoles, oxadiazoles, thiazoles, isothiazoles, thiadiazoles, selenazoles, selenadiazoles, and their benzo analogs - indazoles, benzimidazoles, benzoxazoles, benzisoxazoles, benzoxadiazoles, benzothiazoles, benzoisothiazoles, benzothiadiazoles, benzotriazoles, benzoselenazoles, and ben-zoselenadiazoles has been systematized, summarized, and critically discussed in this monograph. 

Computational studies concerning theoretical approaches to the intrinsic basicity of neutral nitrogen bases have been reported, including those of phos-phoranimines. The non-ionic phosphazene bases BEMP (112), BTPP (113) and (114, R = Ph) appear to be excellent catalysts for the Michael addition reactions. Thus the yield of the coupling reaction of ethyl isocyanoacetate with l,2-bis(4-bromomethylphenyl)ethane is increased by the addition of the phosphazene base BEMP. Polymer-supported BEMP (P-BEMP) has been applied for the allylation of 2H-benzo[d]l,3-dioxolan-5-ol by allyl bromide. " Cyclodehydration of 1,2 diacylhydrazines by tosyl chloride in the presence of P-BEMP leads to excellent yields of 1,3,4,-oxadiazoles. Addition of P-BEMP also improves the yield of the Hofmann elimination step in the synthesis of tertiary mines using REM resin (polymer-bound acrylate ester). ... 

More recently, a solid-phase synthesis of 5-substituted 3-alkylamino-l,2,4-oxadia-zoles has been developed [99]. The method utilizes immobilized N-acyl-lH-benzo-triazole-l-carboximidamides as key intermediates. Cyclization with hydroxylamine under mild conditions furnished the oxadiazole template regioselectively. 

In the mid 1960s, Issidorides and Haddadin addressed some of the limitations in substitution met in earlier reported procedures by developing a synthesis of heteroaromatic A/ oxides that, upon reduction, afford heteroaromatic compounds like phenazine. The Beirut reaction, named after its origin from the capital of Lebanon, involves condensation of benzofurazan oxide (benzo[1,2,5]oxadiazole-1-oxide) and, e.g., enamines, dienes, aldehydes, a,/ -unsaturated ketones, or enolates to form heterocycles... 

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