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Carbocatalysed Oxidative C sp 2 C sp 2 Homocouplings of Benzo‐Fused Heterocycles
Author(s) -
Wirtanen Tom,
Mäkelä Mikko K.,
Sarfraz Jawad,
Ihalainen Petri,
Hietala Sami,
Melchionna Michele,
Helaja Juho
Publication year - 2015
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201500664
Subject(s) - chemistry , catalysis , benzoquinone , x ray photoelectron spectroscopy , stoichiometry , carbon fibers , quinone , combinatorial chemistry , photochemistry , polymer chemistry , organic chemistry , medicinal chemistry , chemical engineering , materials science , composite number , engineering , composite material
Appropriate and fine‐tuned treatments of amorphous carbon (AC) involving aqua regia or concentrated HNO 3 lead to oxidised carbon materials (oAC) which are able to catalyse 2,2′‐ and 3,3′‐homocouplings of various functionalised indoles with outstanding activity. This newly developed carbocatalysed C ${{_{sp{^{2$ C ${{_{sp{^{2$ bond formation can be achieved under mild thermal conditions. The study on the scope of the reaction revealed that the reaction can be extended to the homocoupling of other substrates of high synthetic interest such as 2‐naphthol, 2‐functionalised benzofurans and benzothiofurans. The characterisation of oAC with XPS together with ad hoc experiments aimed at blocking the active site revealed that the presence and distribution of CO functionalities is critical and correlates well with the catalytic activity. Such experiments provide solid support for elucidation of the mechanism, suggesting a quinone nature of the active CO groups, which are spontaneously regenerated by oxygen. This is confirmed by the fact that 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) is able to promote the coupling in a stoichiometric fashion.