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Asymmetric additions to dienes catalysed by a dithiophosphoric acid

2011; Nature Portfolio; Volume: 470; Issue: 7333 Linguagem: Inglês

10.1038/nature09723

1476-4687

Nathan D. Shapiro, Vivek Rauniyar, Gregory L. Hamilton, Jeffrey C.S. Wu, F. Dean Toste,

Asymmetric Hydrogenation and Catalysis

Previous work on nucleophilic additions catalysed by chiral Brønsted acids has been restricted to polarized heteroatom-containing functionalities such as imines, aziridines and carbonyls. This limitation has yet to be overcome despite the fact that acid-catalysed 'Markovnikov' additions to olefins have been known for more than a century. Here the authors show that chiral dithiophosphoric acids can catalyse the intramolecular hydroamination and hydroarylation of dienes and allenes to generate heterocyclic products in exceptional yield and enantiomeric excess. They present a mechanistic hypothesis that involves the addition of the acid catalyst to the diene, followed by SN2′ displacement of the resulting dithiophosphate intermediate. The proposed mechanism is supported by mass spectroscopy and deuterium labelling studies. Here it is shown that chiral dithiophosphoric acids can catalyse the intramolecular hydroamination and hydroarylation of dienes and allenes to generate heterocyclic products in exceptional yield and enantiomeric excess. A mechanistic hypothesis is presented that involves the addition of the acid catalyst to the diene, followed by SN2′ displacement of the resulting dithiophosphate intermediate, and mass spectroscopic and deuterium labelling studies support the proposed mechanism. Chiral Brønsted acids (proton donors) have been shown to facilitate a broad range of asymmetric chemical transformations under catalytic conditions without requiring additional toxic or expensive metals1,2,3,4,5,6,7,8. Although the catalysts developed thus far are remarkably effective at activating polarized functional groups, it is not clear whether organic Brønsted acids can be used to catalyse highly enantioselective transformations of unactivated carbon–carbon multiple bonds. This deficiency persists despite the fact that racemic acid-catalysed 'Markovnikov' additions to alkenes are well known chemical transformations. Here we show that chiral dithiophosphoric acids can catalyse the intramolecular hydroamination and hydroarylation of dienes and allenes to generate heterocyclic products in exceptional yield and enantiomeric excess. We present a mechanistic hypothesis that involves the addition of the acid catalyst to the diene, followed by nucleophilic displacement of the resulting dithiophosphate intermediate; we also report mass spectroscopic and deuterium labelling studies in support of the proposed mechanism. The catalysts and concepts revealed in this study should prove applicable to other asymmetric functionalizations of unsaturated systems.