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Synfacts 2014; 10(8): 0813
DOI: 10.1055/s-0034-1378478
Synthesis of Materials and Unnatural Products
© Georg Thieme Verlag Stuttgart · New York

Efficient Transannular Cyclization via Dearomatization

Contributor(s):
Timothy M. Swager
,
Byungjin Koo
Fukazawa A, * Oshima H, Shimizu S, Kobayashi N, Yamaguchi S. * Nagoya University and Tohoku University, Sendai, Japan
Dearomatization-Induced Transannular Cyclization: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene.

J. Am. Chem. Soc. 2014;
136: 8738-8745
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Publication History

Publication Date:
18 July 2014 (online)

 
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Key words

cyclization - dehydroannulenes - thiophene dioxide

Significance

Transannular cyclization of dehydroannulenes, annulene derivatives containing alkyne moieties, is an attractive way to build polycyclic aromatic hydrocarbons (PAHs). However, dehydroannulenes are highly reactive and thus hard to prepare. Aromatic rings attached to the dehydroannulene, such as 1, confer the stability, but this stabilization sacrifices its reactivity toward cyclization, as shown in the reaction conditions of previous work (80 °C, 9 days). Fukazawa, Yamaguchi, and co-workers oxidized the thiophene moieties in 1 to decrease the aromaticity. As a result, the transannular cyclization proceeds under milder reaction conditions (r.t., 24 h).


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Comment

The oxidation of thiophene was carried out with MCPBA. Another possible reagent for this purpose is Rozen’s reagent (MeCN∙HOF). Thiophene-S,S-dioxide is an interesting n-type, electron-accepting molecule resulting from the lowered LUMO level due to the electron-withdrawing oxygen. This thiophene-S,S-dioxide-fused biphenylene can potentially be a basic skeleton to build more complex n-type PAHs through further modification.


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