Tandem versus single C–C bond forming reaction under palladium–copper catalysis: regioselective synthesis of α-pyrones fused with thiophene

Autor: Manojit Pal, R. Vasu Dev, Bukkapattanam R. Sreekanth, J. Moses Babu, Pazhanimuthu Annamalai, Venkateswara Rao Batchu, Sirisilla Raju, Nalivela Kumara Swamy, Khagga Mukkanti, Krishnamurthi Vyas, P. Rajender Kumar
Rok vydání: 2006
Předmět:
Zdroj: Tetrahedron. 62:9554-9570
ISSN: 0040-4020
DOI: 10.1016/j.tet.2006.07.095
Popis: We herein report a highly convenient protocol for rapid construction of α-pyrone fused with thiophene. This includes one-pot and regioselective synthesis of 4,5-disubstituted and 5-substituted thieno[2,3- c ]pyran-7-ones, 6,7-disubstituted and 6-substituted thieno[3,2- c ]pyran-4-ones. The synthesis of thieno[2,3- c ]pyran-7-ones involves palladium mediated cross coupling of 3-iodothiophene-2-carboxylic acid with terminal alkynes in a simple synthetic operation. The coupling–cyclization reaction was initially studied in the presence of Pd(PPh 3 ) 2 Cl 2 and CuI in a variety of solvents. 5-Substituted 4-alkynylthieno[2,3- c ]pyran-7-ones were isolated in good yields when the reaction was performed in DMF. Similarly, 6-substituted 7-alkynylthieno[3,2- c ]pyran-4-ones were synthesized via palladium-catalyzed cross coupling of 2-bromothiophene-3-carboxylic acid with terminal alkynes. A tandem C–C bond forming reaction in the presence of palladium catalyst rationalizes the formation of coupled product in this apparently three-component reaction. The cyclization step of this coupling–cyclization–coupling process occurs in a regioselective fashion to furnish products containing six-membered ring only. This sequential C–C bond forming reaction however, can be restricted to the formation of single C–C bond by using 10% Pd/C–Et 3 N–CuI–PPh 3 as catalyst system in the cross coupling reaction. 5-Substituted thieno[2,3- c ]pyran-7-ones were obtained in good yields when the coupling reaction was performed under this condition. Some of the compounds synthesized were tested in vitro for their anticancer activities.
Databáze: OpenAIRE
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