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Combined Experimental and Computational Investigations of Rhodium‐Catalysed CH Functionalisation of Pyrazoles with Alkenes
Author(s) -
Algarra Andrés G.,
Davies David L.,
Khamker Qudsia,
Macgregor Stuart A.,
McMullin Claire L.,
Singh Kuldip,
VillaMarcos Barbara
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201405550
Subject(s) - methyl vinyl ketone , styrene , chemistry , methyl acrylate , rhodium , dimer , catalysis , acrylate , oxidative coupling of methane , density functional theory , medicinal chemistry , aryl , ketone , stereochemistry , polymer chemistry , organic chemistry , copolymer , polymer , computational chemistry , alkyl
Abstract Detailed experimental and computational studies have been carried out on the oxidative coupling of the alkenes C 2 H 3 Y (Y=CO 2 Me ( a ), Ph ( b ), C(O)Me ( c )) with 3‐aryl‐5‐R‐pyrazoles (R=Me ( 1 a ), Ph ( 1 b ), CF 3 ( 1 c )) using a [Rh(MeCN) 3 Cp*][PF 6 ] 2 /Cu(OAc) 2 ⋅ H 2 O catalyst system. In the reaction of methyl acrylate with 1 a , up to five products ( 2 aa – 6 aa ) were formed, including the trans monovinyl product, either complexed within a novel Cu I dimer ( 2 aa ) or as the free species ( 3 aa ), and a divinyl species ( 6 aa ); both 3 aa and 6 aa underwent cyclisation by an aza‐Michael reaction to give fused heterocycles 4 aa and 5 aa , respectively. With styrene, only trans mono‐ and divinylation products were observed, whereas with methyl vinyl ketone, a stronger Michael acceptor, only cyclised oxidative coupling products were formed. Density functional theory calculations were performed to characterise the different migratory insertion and β‐H transfer steps implicated in the reactions of 1 a with methyl acrylate and styrene. The calculations showed a clear kinetic preference for 2,1‐insertion and the formation of trans vinyl products, consistent with the experimental results.