BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene-type, Diels-Alder, as well as cascade and multi-component reactions.
The origin of the single chirality of most biomolecules is still a great puzzle. Carbohydrates could form in the formose reaction, which is proposed to be autocatalytic and contains aldol reaction steps. Based on our earlier observation of organoautocatalysis and spontaneous enantioenrichment in absence of deliberate chiral influences in the aldol reaction of acetone and p-nitrobenzaldehyde we suggest that a similar effect might be present also in the aldol reactions involved in gluconeogenesis. Herein we show that reactant precipitation observed in our earlier reported experiments does not affect the asymmetric autocatalysis in the aldol reaction we studied. We explain the phenomenon of spontaneous mirror symmetry breaking in such organocatalytic homogenous systems qualitatively by non-linear reaction network kinetics and classical transition state theory.
The enantioselective BINOL-phosphate catalyzed formation of a quaternary carbon center, bearing a N-atom has been achieved through the self-coupling reaction of enamides; the corresponding products have been isolated in up to >99% ee and their application for the synthesis of versatile synthetic building blocks-beta-aminoketones-has been demonstrated.
Keywords: Organocatalysis / Brønsted acids / Lewis acids / Hydrogen bonds / Binaphthyl derivativesIn recent years, binaphthyl compounds have found frequent applications in the design of various asymmetric organocatalysts, because binaphthyl structures are an attractive platform for organocatalyst development, particularly in light of their axial chirality characteristic. In this review, we discuss
A first organocatalytic enantioselective route was developed for the conversion of readily prepared and air stable aliphatic hydrazones to synthetically valuable alpha-hydrazinonitriles. This BINOL-phosphate catalyzed Strecker-type reaction (see scheme, Ar = p-NO(2)-Ph) provides a new practical and direct route to alpha-hydrazino acids of synthetic and biological importance. The actually active catalyst is proposed to be an in situ formed O-silylated BINOL-phosphate, thus shifting the nature of catalysis from Brønsted acid to Lewis acid organocatalysis.
A first and fairly mild metal-free catalytic route was developed for the [3+2] cycloadditions of different N-acylhydrazones to cyclopentadiene, providing the synthetically and biologically important five-membered cyclic compounds pyrazolidines. The reaction was successfully conducted in high yields (up to 99 %) with high diastereoselectivities (up to 98:2 dr) by using catalytic amounts of TMSOTf (trimethylsilyl
A facile enantioselective synthesis of chiral pyrazolidines via a [3+ 2] cycloaddition reaction, involving a BINOL-derived phosphoric acid and an in situ generated BINOL phosphate-derived silicon Lewis acid, which may act cooperatively, has been developed.
A scalable, asymmetric synthesis of (3aS,6aS)-6a-(5-bromo-2-fluorophenyl)-1-((R)-1-phenylpropyl)tetrahydro-1H,3H-furo [3,4-c]isoxazole, a key intermediate in the synthesis of LY2886721, is reported. Highlights of the synthesis include the development of an asymmetric [3 + 2] intramolecular cycloaddition facilitated by trifluoroethanol, and the development of a new synthesis of (R)-N-(1-phenylpropyl)hydroxylamine tosylate which proceeds through a p-anisaldehyde imine and avoids the formation of toxic hydrogen cyanide gas as a byproduct. The synthesis proceeds over four steps and provides the product in 36% overall yield.
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