ABACCR

Asymmetric Brønsted Acid Catalysed Cyclisation Reactions

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 Obiettivo del progetto (Objective)

'We wish to develop new asymmetric Brønsted acid catalysed cyclisation reactions that will allow the efficient and highly enantioselective construction of azabicyclic structures from readily available starting materials. This will constitute a new, powerful and broadly applicable organocatalytic asymmetric strategy to such target molecules. Conceptually our proposal is to exploit the high reactivity of N-acyl iminium ions in cyclisation reactions within the asymmetric environment of an associated conjugate base of a chiral Brønsted acid (HA*). For enantioselective N-acyl iminium ion cyclisations, a keto amide starting material with a suitable pi-nucleophile attached to the nitrogen atom of the amide is required. The reaction is technically trivial to perform; a solution of the keto amide starting material is treated with a catalytic quantity of an ‘effective’ chiral Brønsted acid. Loss of water should result in the formation of an N-acyl iminium ion, which, in a low polarity solvent, should be (tight) ion paired with the chiral conjugate base of the Brønsted acid. Provided there is sufficient ordering and effective facial differentiation in the ion pair, attack of the pendant pi-nucleophile will give rise to enantioselectivity in the (irreversible) cyclisation step. During the course of the Fellowship, through physical organic chemistry techniques and molecular modelling calculations we would like to elucidate the mechanistic pathway and origins of stereocontrol in the new catalytic asymmetric methods we are developing. Finally we wish to apply the developed chemistry as a key carbon-carbon bond forming step in the total asymmetric synthesis of an indole alkaloid natural product. Therefore this multidisciplinary Fellowship project will involve the development of innovative asymmetric organic methods, physical organic chemistry, computational chemistry and target synthesis.'