Dehydrative Nazarov-type electrocyclizations of alkenyl (hetero)aryl carbinols via calcium catalysis: Access to cyclopenta[b]thiophenes and indene derivatives

TETRAHEDRON

卷:73

Article

Martin, M. Cynthia¹  Sandridge, Matthew J.¹  Williams, Corey W.¹  Francis, Zola A.¹  France, Stefan^1,2 

[1] Georgia Inst Technol, Sch Chem & Biochem, Atlanta, GA 30332 USA

[2] Georgia Inst Technol, Petit Inst Bioengn & Biosci, Atlanta, GA 30332 USA

关键词: Electrocyclization;    Heterocycles;    Cyclopentathiophenes;    Calcium catalysis;    Carbinols;    Nazarov cyclizations;   

DOI  :  10.1016/j.tet.2017.03.041

来源: Elsevier

【 摘 要 】

A general approach to the understudied cyclopenta[b]thiophenes is reported. The products were directly generated from calcium-catalyzed, dehydrative, Nazarov-type electrocyclizations of alkenyl thienyl carbinols in up to 82% yield. The thienyl carbinols demonstrated good tolerance for aryl and heteroaryl substituents on the alkene. Aryl carbinols were also amenable to the calcium-catalyzed conditions and afforded indene derivatives in good yields. In most cases, the reaction was selective for the thermodynamic alkene isomer; however, substituent effects played a role in determining product outcomes. Mechanistically, the calcium catalyst initiated formation of alkenyl (hetero)aryl carbinyl cations which subsequently underwent a 4 pi electrocyclization and elimination that is reminiscent of the Nazarov reaction. This transformation is significant for two main reasons: 1) it represents one of the only examples of catalysis for dehydrative, Nazarov-type electrocyclizations in which thiophene was compatible; 2) it allowed for the direct formation of cyclopenta[b]thiophenes while circumventing the need for cyclopenta [b]thiophenones as precursors. (C) 2017 Published by Elsevier Ltd.

【 授权许可】

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