Isomerisation versus carbonylative pathways in the hydroxy-carbonylation, methoxy-carbonylation, and amino-carbonylation of N-tosyl-3-pyrroline
Abstract
The reactivity of N-tosyl-3-pyrroline is significantly lower than that of mono-substituted alkenes in Pd catalysed methoxycarbonylation reactions. For example, most bulky diphosphine/ Pd catalysts, including the well-known Pd catalyst derived from 1,2-bis(di-tert-butylphosphino)xylene (DTBPX), were found to give no product at all in the methoxycarbonylation of N-tosyl-3-pyrroline. The competing pathways in methoxycarbonylation of N-methane-sulfonyl-3-pyrroline using Pd/ DTBPX were studied using DFT calculations; these show that the coordination of the alkene is unfavourable, and once coordinated, isomerisation is a lower energy pathway that ultimately leads to an alternative product. Experimentally a side product resulting from alkene isomerisation and addition of methanol is formed slowly (if CO is present), and rapidly if CO is not. A less bulky derivative of DTBPX forms the required alkene complex with much lower barriers. A study has been made of the enantioselective carbonylation of N-tosyl-3-pyrroline using water, methanol or aniline as nucleophile. This study revealed that there is a range of possible products with most of these initiated by a Pd-catalysed isomerisation of the alkene. Using less bulky members of the Pd/Phanephos family of catalysts, it is possible to produce the methoxycarbonylation product from this poorly reactive alkene with reasonably good chemoselectivity and around 80% e.e. at higher pressures of CO.
Citation
Fuentes García , J A , Durrani , J , Leckie , S M , Crawford , L , Buehl , M & Clarke , M 2016 , ' Isomerisation versus carbonylative pathways in the hydroxy-carbonylation, methoxy-carbonylation, and amino-carbonylation of N -tosyl-3-pyrroline ' , Catalysis Science & Technology , vol. 6 , no. 20 , pp. 7477-7485 . https://doi.org/10.1039/C6CY01268J
Publication
Catalysis Science & Technology
Status
Peer reviewed
ISSN
2044-4753Type
Journal article
Description
The authors thank the EPSRC for funding, primarily from grant number EP/M003868/1.Collections
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