Oxazaborolidine-mediated asymmetric reduction of 1,2-diaryl-2-benzyloxyiminoethanones and 1,2-diarylethanediones

Cr-Catalyzed Asymmetric Cross Aza-Pinacol Couplings for β-Amino Alcohol Synthesis

Chiral β-amino alcohols are crucial structural motifs found in pharmaceuticals, natural products, and chiral ligands in asymmetric catalysis. Despite previous advances, the development of catalytic approaches to access β-amino alcohols bearing vicinal stereocenters from readily available chemicals remains a prominent challenge. Herein, we describe the Cr-catalyzed asymmetric cross aza-pinacol coupling of aldehydes and N-sulfonyl imines. This protocol proceeds in a radical-polar crossover manner from the intermediacy of an α-amino radical instead of a ketyl radical. Key to the success is using a chiral chromium catalyst, which plays a triple role in the chemoselective single-electron reduction of the imine, fast radical interception to inhibit radical addition to imines, and chemo- and stereoselective addition to aldehydes instead of imines. This method provides a modular and efficient approach to accessing diverse β-amino alcohols bearing vicinal stereocenters.

N-Alkylation/aldol reaction of α-aldimino thioesters: a facile three-component coupling reaction

Theoretical calculation of the reactivity of α-imino thioesters indicates that they are very reactive substrates for Umpolung N-alkylation. In fact, treatment of α-aldimino thioesters with dialkylzinc reagents in the presence of aldehydes or imines gives three-component coupling products in good yields.

2,3-Dimethoxy-2,3-dimethyl-1,4-dioxane as a useful precursor to 2,3-dimethylene-1,4-dioxane for [4+2] cycloaddition reaction

2,3-Dimethoxy-2,3-dimethyl-1,4-dioxane readily prepared from biacetyl serves as a stable precursor to 2,3-dimethylene-1,4-dioxane which undergoes a [4+2] cycloaddition reaction with dienophiles to give functionalized cyclohexene derivatives. The cycloaddition adducts obtained by the present procedure are transformed into potentially useful intermediates for biologically important materials.

2,3-Dimethoxy-2,3-dimethyl-1,4-dioxane serves as a stable precursor to 2,3-dimethylene-1,4-dioxane which undergoes a cycloaddition with dienophiles. The adducts are transformed into useful intermediates for biologically important materials.

Highly enantioselective borane reduction of heteroaryl and heterocyclic ketoxime ethers catalyzed by novel spiroborate ester derived from diphenylvalinol: application to the synthesis of nicotine analogues

An asymmetric synthesis for the preparation of nonracemic amines bearing heterocyclic and heteroaromatic rings is described. A variety of important enantiopure thionyl and arylalkyl primary amines were afforded by the borane-mediated enantioselective reduction of O-benzyl ketoximes using 10% of catalyst 10 derived from ( S)-diphenylvalinol and ethylene glycol with excellent enantioselectivity, in up to 99% ee. The optimal condition for the first asymmetric reduction of 3- and 4-pyridyl-derived O-benzyl ketoxime ethers was achieved using 30% of catalytic loading in dioxane at 10 degrees C. ( S)- N-ethylnornicotine ( 3) was also successfully synthesized from the TIPS-protected ( S)-2-amino-2-pyridylethanol in 97% ee.

HPLC on chiral support with polarimetric detection: Application to conglomerate discovery

In conglomerates, each single crystal contains only one of the two possible enantiomeric forms--either dextrorotatory or levorotatory. The analysis of a single crystal by liquid chromatography on chiral support associated with chiroptical detection is a very efficient tool to reveal the occurrence of a conglomerate. In terms of rapidity and easiness, this method compares favorably with the classical methods used to show this occurrence. Two examples are provided.

Stereocontrolled Reactions Mediated by a Remote Sulfoxide Group: Synthesis of Optically Pure anti-β-Amino Alcohols

[reaction: see text] A one-step synthesis of enantiomerically pure anti-1,2-amino alcohol derivatives has been achieved by reaction of prochiral oxygenated 2-p-tolylsulfinylbenzyl carbanions with N-sulfinylimines bearing the same configuration at sulfur.

Single route to chiral syn- and anti-2-amino-1,2-diphenylethanols via a new stereodivergent opening of trans-1,2-diphenyloxirane

Oxiranyl ring opening of trans-stilbene oxide gave rise to anti- or syn-2-bromo-1,2-diphenylethanols, using either MgBr(2).Et(2)O or MgBr(2).Et(2)O, NaBr, and KBr with Amberlyst 15, respectively. Starting from optically pure (R,R)-trans-stilbene oxide, (1R,2R)- and (1R,2S)-2-amino-1,2-diphenylethanols were obtained in high yield and ee.