Issue in Honor of Prof. Oleg Kulinkovich ARKIVOC 2008 (ix) 140-148 Highly regioselective Synthesis of 1-(5-Trichloromethyl -5-hydroxy - 4,5-dihydroisoxazole-3-methylene)-5-phenyl-1H-1,2,3-triazoles Marcos A. P. Martins,* a Daniel J. Emmerich, b Adilson P. Sinhorin, c Marcelo Rossatto, a Clarissa P. Frizzo, a Helio G. Bonacorso, a and Nilo Zanata a a Núcleo de Química de Heterociclos (NUQUIMHE), Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brasil b Departamento de Química, Universidade Regional Integrada do Alto Uruguai e das Missões, Erechim, RS, Brasil; Departamento de Química, c Universidade Federal do Mato Grosso, Sinope, MT, Brasil E-mail: mmartins@base.ufsm.br Dedicated to Prof. Oleg Kulinkovich on the occasion of his 60 th birthday Abstract A convenient method to obtain a series of 1-(5-hydroxy-5-trichloromethyl-4,5-dihydroisoxazole- 3-methylene)-5-phenyl-1H-1,2,3-triazoles by a regiospecific cycloaddition reaction of phenyl acetylenes [Ph–C≡C–R, where R = C(O)CCl 3 , C(O)CHCl 2 , C(OH) 2 CF 3 , CCl 3 and 3- methylisoxazolo-5-carbonyl] with 5-hydroxy-5-trichloromethyl-4,5-dihydroisoxazole-3- methylene azide is reported, in moderate to good yields (67-80%). From the reaction of a 4- trichloroacetyltriazole derivative with methanol or methylamine it was possible to obtain the corresponding ester and amide derivatives, respectively, by substitution of the trichloromethyl group. Keywords: 1,2,3-Triazoles, cycloadditions, azides, trihalomethyl compounds Introduction 1,2,3- Triazoles are nitrogen heteroarenes which have a range of important applications in the pharmaceutical and agricultural industries 1 The most widely used method for the synthesis of 1,2,3-triazoles, pioneered by Huisgen, involves the thermal 1,3-dipolar cycloaddition of organic azides with alkynes. 2 The 1,3-dipolar cycloaddition of azides to alkynes is a versatile route to obtain 1,2,3-triazoles, 3 the progress in this area has been reviewed periodically. 4 The main challenge associated to this reaction is a regioisomeric mixture of products when unsymmetrical alkynes are used. Recently, the so-called ‘click chemistry’, establishing heteroatom linkages ISSN 1551-7012 Page 140 © ARKAT USA, Inc.