In this paper, we describe the use of p-TSA based Deep Eutectic Solvents (DESs) as alternative environmental-friendly “active” solvents for the microwave-mediated synthesis of 6-substituted 3,4-fused 2-pyranones, and in particular isocoumarins, starting from 2-alkynyl-(hetero)arylcarboxylates. When the alkyne terminus bears a neutral or an electron-donating group (EDG), the reactions are fast, clean and highly regioselective, to give the 6-endo-dig cyclization products in good to excellent yields. For substrates bearing an electron-withdrawing group (EWG) on the alkyne end, the regioselectivity can be tuned by adding a small amount of silver(I) triflate as co-catalyst. DES was demonstrated to be reusable without loss of efficiency in terms of reaction yields. Based on experimental evidences and previous findings, two competitive mechanisms working simultaneously are proposed to explain the outcomes and the regioselectivity issues.
p-TSA-Based DESs as “Active Green Solvents” for Microwave Enhanced Cyclization of 2-Alkynyl-(hetero)-arylcarboxylates: an Alternative Access to 6-Substituted 3,4-Fused 2-Pyranones / F. Curti, M. Tiecco, V. Pirovano, R. Germani, A. Caselli, E. Rossi, G. Abbiati. - In: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY. - ISSN 1434-193X. - 2019:9(2019), pp. 1904-1914.
|Titolo:||p-TSA-Based DESs as “Active Green Solvents” for Microwave Enhanced Cyclization of 2-Alkynyl-(hetero)-arylcarboxylates: an Alternative Access to 6-Substituted 3,4-Fused 2-Pyranones|
ABBIATI, GIORGIO (Corresponding)
|Parole Chiave:||Deep eutectic solvents; Microwave chemistry; Ionic liquids; Cyclization; Alkynes|
|Settore Scientifico Disciplinare:||Settore CHIM/06 - Chimica Organica|
|Data di pubblicazione:||2019|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1002/ejoc.201801884|
|Appare nelle tipologie:||01 - Articolo su periodico|
File in questo prodotto:
|EJOC_2019_Abbiati_DES_post-print.pdf||Post-print||Post-print, accepted manuscript ecc. (versione accettata dall'editore)||Open Access Visualizza/Apri|
|EJOC_2019_Supporting_Information_Abbiati_DES.pdf||Supporting Information (NMR spectra of all products)||Altro||Open Access Visualizza/Apri|
|Curti_et_al-2019-European_Journal_of_Organic_Chemistry.pdf||Reprint - versione editoriale||Publisher's version/PDF||Administrator Richiedi una copia|