1. Absence of intermediates in the BINOL-derived mg(ii)/phosphate-catalyzed desymmetrizative ring expansion of 1-Vinylcyclobutanols
- Author
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Estefania Capel, Marta Rodríguez-Rodríguez, Uxue Uria, Manuel Pedron, Tomas Tejero, Jose L. Vicario, Pedro Merino, Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), European Commission, Eusko Jaurlaritza, Gobierno de Aragón, Ministerio de Economía y Competitividad (España), and Universidad del País Vasco
- Subjects
basis-sets ,pinacol rearrangement ,topological analysis ,semipinacol rearrangement ,access ,density functionals ,electron localization function ,Organic Chemistry ,thermochemistry ,acid ,bromination ,Article - Abstract
The catalyzed desymmetrizative ring expansion of alkenylcyclobutanols promoted by halofunctionalization of the alkene moiety with N-bromosuccinimide has been experimentally and computationally studied. The reaction yields highly enantioenriched cyclopentanones bearing two all-carbon quaternary stereocenters, one of them being generated in the rearrangement of the cyclobutane ring and the other by enantioselective desymmetrization. The reaction is competitive with the formation of a spiroepoxide, but it turns completely selective toward the cyclopentanone when a chiral bisphosphonium magnesium salt is employed as a catalyst. Mechanistic studies support the formation of an ion pair leading to a complex with only a unit of phosphoric acid, which is the resting state of the catalytic cycle. Calculations reproduce in an excellent way the observed reactivity and predict the effect exerted by the substituents of the aromatic ring linked to the double bond. The computational studies also revealed the reaction as a highly asynchronous concerted process taking place as one kinetic step but in two stages: (i) halogenation of the double bond and (ii) rearrangement of the cyclobutane. No intermediates are present in the reaction as energy minima. The experimental scope of the reaction further confirms the predictions for the observed reactivity and selectivity., This research was supported by the Spanish MICIU (PID2019-104090RB-100, FEDER-CTQ2016-76155-R, and FEDER-PID2020-118422GB-I00), the Basque Government (Grupos IT908-16), UPV/EHU (fellowship to E.C. and M.R.-R.), and the Government of Aragón (Grupos Consolidados, E34_20R and a fellowship to M.P.).
- Published
- 2021