Articolo in rivista, 2016, ENG, 10.1002/ejoc.201600897

Competitive Copper Catalysis in the Condensation of Primary Nitro Compounds with Terminal Alkynes: Synthesis of Isoxazoles

Baglieri A.; Meschisi L.; De Sarlo F.; Machetti F.

Istituto di chimica dei composti organometallici, c/o Dipartimento di chimica Ugo Schiff, Consiglio nazionale delle ricerche (CNR), Via della Lastruccia 13, Sesto Fiorentino, Firenze, 50019, Italy; Dipartimento di chimica Ugo Schiff, Università degli studi di Firenze, Via della Lastruccia 13, Sesto Fiorentino, Firenze, 50019, Italy

Isoxazoles, mainly 3,5-disubstituted, are prepared by catalytic condensation of primary nitro compounds with terminal acetylenes by using a copper/base catalytic system. The additional catalytic effect of the copper(II) salts is evidenced by comparing the kinetic profiles. Selectivity dependence on reaction conditions is considered for phenylacetylene in the following competitive processes: oxidative coupling of terminal alkynes to conjugated diynes catalyzed by CuII and base in the presence of air; production of furazans beside condensation with benzoylnitromethane to 3-benzoylisoxazoles, as a result of the reaction of the dipolarophile with 3,4-dibenzoylfuroxan; addition of electron-poor alkynes (e.g., methyl propiolate) with themselves and with the nitro compound. Thus, oxidative coupling is negligible in reactions with "active" nitro compounds, whereas with nitroalkanes both products are observed: only trace amounts of isoxazoles are detected without copper. Similarly, in the presence of copper, 3-benzoyl-5-phenylisoxazole is predominant over the furazan. Furthermore, condensations of electron-poor alkynes give complex reaction mixtures in the presence of base alone, but cycloadducts are conveniently prepared with copper. The results indicate the practical and general utility of this catalytic method for synthetic practice.

European journal of organic chemistry (Print) 2016 (27), pp. 4643–4655

Keywords

Alkynes, Copper, Homogeneous catalysis, Nitro compounds, Nitrogen heterocycles

CNR authors

Machetti Fabrizio

CNR institutes

ICCOM – Istituto di chimica dei composti organo metallici

ID: 360130

Year: 2016

Type: Articolo in rivista

Creation: 2016-11-03 08:56:31.000

Last update: 2021-04-14 10:29:28.000

External IDs

CNR OAI-PMH: oai:it.cnr:prodotti:360130

DOI: 10.1002/ejoc.201600897

Scopus: 2-s2.0-84988350472