Five-membered Systems with More than Two Heteroatoms

Five-membered Systems with More than Two Heteroatoms 

In the preparation of novel 1,3,4-oxadiazoles 25 from 1,2-diacylhydrazines 24, Brain et al. used a highly efficient cyclodehydration assisted by use of microwaves, 

Microwave irradiation coupled with poly(ethylene glycol)-supported Burgess reagent reduced the reaction time to 2-4 min and led to improved yields. Use of harsh reagents (e.g. SOCI2, POCI3, and polyphosphoric acid) for the cyclodehydration was avoided. 

The tetrazole functional group is of particular interest in medicinal chemistry, because of its potential role as a bioisostere of the carboxyl group. In this context, Schulz et al. have demonstrated the synthetic utility of the cyano group of arylni-trile boronates as a source of tetrazole derivatives under microwave conditions. The reaction is conducted with azidotrimethylsilane and dibutyltin oxide as catalyst to provide aryltetrazole boronates in yields ranging from 60 to 93% [56]. In the same manner, microwaves may assist successful conversion of sterically hindered nitriles into tetrazoles [57]. 

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Five-membered Systems with More than Two Heteroatoms - Synthesis of Triazoles and Related Compounds... 

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