Recent advances in asymmetric reactions using sulfinimines (N-sulfinyl imines)

Stereoselective synthesis of azetidines and pyrrolidines from N-tert-butylsulfonyl(2-aminoalkyl)oxiranes

Base-induced cyclization of enantiopure (2-aminoalkyl)oxiranes allowed the stereospecific formation of pyrrolidin-3-ols and/or 2-(hydroxymethyl)azetidines, depending on the reaction conditions. The oxidation of 2-(hydroxymethyl)azetidines led to azetidine-2-carboxylic acids in high yields.

Asymmetric synthesis of (2S,3R)-(-)-epi-CP-99,994 using sulfinimine-derived anti-2,3-diamino esters

A differentially protected C-3 N-sulfinyl, C-2 N,N-(diphenylmethylene) 2,3-diamino ester was employed in the synthesis of the amino piperidine (2S,3R)-(-)-epi-CP-99,994. Key steps in the synthesis included the chemoselective hydrolysis of the C-2 N,N-(diphenylmethylene) group and its reprotection as a dibenzylamino group.

Asymmetric synthesis of acyclic 1,3-amino alcohols by reduction of N-sulfinyl beta-amino ketones. Formal synthesis of (-)-pinidinol and (+)- epipinidinol

Stereoselective reduction of acyclic N-sulfinyl beta-amino ketones with (LiEt(3)BH) and Li(t-BuO)(3)AlH, respectively, gave anti- and syn-1,3-amino alcohols with excellent selectivity. A formal asymmetric synthesis of the hydroxy piperidine alkaloids (-)-pinidinol and (+)-epipinidinol from a common N-sulfinyl beta-amino ketone ketal precursor was developed. The pinidinol piperidine ring was formed via a novel acid-catalyzed cascade reaction of a N-sulfinylamino silyl protected alcohol ketal.

Asymmetric synthesis of aminochromanes via intramolecular indium-mediated allylation of chiral hydrazones

The asymmetric intramolecular indium-mediated cyclization reaction delivers chromanes with excellent diastereoselectivity (68-91% yield, dr >99:1). The reaction was efficient for aryl substrates with both electron-withdrawing and -donating groups. Carboxylic acid additives were found to be necessary for optimal reaction.

Synthetic method for the preparation of 2-aminomethyl-1,3-diene derivatives through indium-mediated 1,3-butadien-2-ylation of imines

An efficient method for the preparation of a variety of 2-aminomethyl-1,3-dienes was developed through the reaction of imines with organoindium reagent generated in situ from indium and 1,3-dibromo-2-butyne. Three-component reactions of aldehydes, amines, and organoindium reagents gave successful results in a one-pot process.

Vinylaluminum addition to sulfinimines (N-sulfinyl imines). Asymmetric synthesis of anti-alpha-alkyl beta-amino esters

Addition of vinylaluminum NMO reagents to N-(p-toluenesufinyl)- and N-(2-methypropanesulfinyl)-derived sulfinimines gives N-sulfinyl aza-Morita-Baylis-Hillman products (dr = 7:1 to 12:1) that result from addition of the reagent from the least hindered direction. Hydrogenation of the aza-MBH adducts with a Rh(I) catalyst affords anti-alpha-substituted N-sulfinyl-beta-amino esters in good yield and high dr (10:1 to 21:1).

tert-Butanesulfinimines: structure, synthesis and synthetic applications

Since Ellman's seminal works, over the past ten years tert-butanesulfinimines have proved to be useful chiral amino intermediates for organic synthesis. Through highly stereoselective reactions, amongst which reductions, nucleophilic 1,2-additions and ylide condensations, a broad range of nitrogen-containing compounds has been synthesized. Although the stereoselectivity levels are high in most cases, the sense of the stereoinduction is generally not predictable. The object of this critical review is to present the models proposed to rationalize the stereochemical outcome of the reactions involving tert-butanesulfinimines and to point out an obvious lack of homogeneity amongst them (128 references).

Monoalkylation of primary amines and N-sulfinylamides

An efficient monoalkylation of primary amines with primary or secondary alcohols catalyzed by Ra-Ni under mild conditions is described.

Total synthesis of siomycin A: construction of synthetic segments

The five practical segments for the total synthesis of siomycin A, that is, the dehydropiperidine segment A (5), the pentapeptide segment B (3), the dihydroquinoline segment C (6), and the beta-phenylselenoalanine dipeptide segments D (7) and E (4), were synthesized. Segment A (5) was constructed by the coupling of the azomethine ylide and the chiral sulfinimine, followed by the stereoselective reduction of the six-membered imine function. Segment B (3) was synthesized by the phenylselenylation of the beta-lactone, stereoselective vinylzinc addition to the chiral sulfinimine, and oxazoline-thioamide conversion. Segment C (6) was prepared by the one-pot olefination of the tetrahydroquinoline N-oxide using triflic anhydride and triethylamine, stereoselective reduction of the methyl ketone function, and regioselective Yb(OTf)(3)-catalyzed epoxide opening by the amino group. Segments D (7) and E (4) were synthesized by coupling of the properly protected beta-phenylselenoalanines.

Studies on the Bisoxazoline and (-)-Sparteine Mediated Enantioselective Addition of Organolithium Reagents to Imines

The enantioselective addition of organolithium reagents to N-anisyl aldimines promoted by chiral bisoxazolines and (-)-sparteine as external ligands is described. This reaction proceeds readily with a wide range of aldimine substrates (aliphatic, aromatic, olefinic) and organolithium nucleophiles (Me, n-Bu, Ph, vinyl) in excellent yields (81-99%) and with high enantioselectivities (up to 95.5:4.5 er). The external ligands can be used in substoichiometric amounts albeit with slightly attenuated enantioselectivities. A systematic evaluation of the structural features of the bisoxazolines revealed a primary contribution from the substituent at C(4) and a secondary influence from the bridging substituents. A computational analysis (PM3) provided a clear rationalization for the origin of enantioselectivity.