Gao H, Connors DM, Goroff NS. Synthesis of Phenanthro[9,10-c]thiophenes by 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-Promoted Cyclo-Oxidation.
Chempluschem 2020;
84:630-633. [PMID:
31944022 DOI:
10.1002/cplu.201900099]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 04/25/2019] [Indexed: 11/11/2022]
Abstract
A new method to prepare phenanthro[9,10-c]thiophenes has been developed. In the presence of triflic acid, 3,4-diaryl thiophenes undergo 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-promoted cyclo-oxidation. NMR and computational studies indicate that protonation of the thiophene plays a key role in this reaction. The reaction can be used to prepare phenanthro[9,10-c]thiophene, as well as derivatives with alkyl, bromo, and methoxy substituents. However, the yields and selectivity of the reaction depend on both the nature and location of the substituents. Bis(3-methoxyphenyl)thiophene reacts under these conditions to give the desired product in 57 % yield, while bis(4-methoxyphenyl)thiophene gives no product. Bis(3-bromophenyl)thiophene did not react, but cyclo-oxidation of bis(4-bromophenyl)thiophene provides the desired product in 34 % yield.
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