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Relevant academic research and scientific papers

A surprising mechanistic "switch" in Lewis acid activation: A bifunctional, asymmetric approach to α-hydroxy acid derivatives

We report a detailed synthetic and mechanistic study of an unusual bifunctional, sequential hetero-Diels-Alder/ring-opening reaction in which chiral, metal complexed ketene enolates react with o-quinones to afford highly enantioenriched, α-hydroxylated carbonyl derivatives in excellent yield. A number of Lewis acids were screened in tandem with cinchona alkaloid derivatives; surprisingly, trans-(Ph3P)2PdCl2 was found to afford the most dramatic increase in yield and rate of reaction. A series of Lewis acid binding motifs were explored through molecular modeling, as well as IR, UV, and NMR spectroscopy. Our observations document a fundamental mechanistic "switch", namely the formation of a tandem Lewis base/Lewis acid activated metal enolate in preference to a metal-coordinated quinone species (as observed in other reactions of o-quinone derivatives). This new method was applied to the syntheses of several pharmaceutical targets, each of which was obtained in high yield and enantioselectivity.

Enzyme-mediated synthesis of (R)- and (S)-α-ionone

Diastereoisomeric enrichment through fractional crystallisation of 4-nitrobenzoate derivatives of α-ionol, and enantioselective enzyme-mediated reactions of α-ionol and α-ionol acetate, were usefully combined to optimise two different procedures to enantiopure (S)- and (R)-ionone.

Novel Electronic Effects of Remote Substituents on the Oxazaborolidene Catalyzed Enantioselective Reduction of Ketones

A new class of hihgly enantioselective oxazaborolidine-catalyzed reductions of achiral ketones is reported which depends on steroelectronic effects involving p-substituted non-planar aromatic ketones, or ?-coordinated transition-metal containing ketones, or strained ring ketones, as exemplified in Table 1.The discovery of these reactions was guided by the transition state model 1, for which they provide experimental support.Because high enentioselectivities (>30:1) are achievable, these reductions define an excellent method for the synthesis of, for example, chiral benzhydrols, chiral propargylic, or chiral allylic alcohols.Lower enantioselectivities observed with CH2Cl2 as solvent, relative to toluene as solvent, are consistent with the transition-state model 1 and indicate that CH2Cl2 hydrogen bonds to the donor groups in the ?-electron-rich carbonyl substituent (RL in 1) thereby diminishing electron supply.

ENANTIO- AND STEREOSELECTIVE SYNTHESES OF THE DIHYDROXYOCTADIENOIC ACID FRAGMENTS OF THE RORIDINS AND TRICHOVERRINS

Syntheses of protected versions of the dihydroxyoctadienoic acid fragments corresponding to roridin A and trichoverrin B are described.