Asymmetric Synthesis of Terminal N-tert-Butylsulfinyl Aziridines from Organoceriums and an α-Chloroimine

A Three Component Protocol for the Synthesis of Aziridines using BF3·(OEt)2

Synthesis of N-(1R,2S)-2-(bromo-3-oxo-1,3-diphenylpropyl)-4-methylbenzene sulfonamide and N-(1R,2S)-(2-bromo-3-oxo-1,3-diphenylpropyl)-4-methylbenzene sulfonamide was carried out by a three component reaction using phenacyl bromide, p-toluenesulfonamide and carboxyaldehyde in presence of mild Lewis acid such as BF3·(OEt)2 in dichloromethane. The synthetic utility of this protocol was carried out with syn-isomer to yield corresponding cis-aziridines. This protocol was operationally simple for a wide variety of substituted carboxaldehydes and substituted phenacyl bromides.

Palladium-Catalyzed Aerobic Anti-Markovnikov Oxidation of Aliphatic Alkenes to Terminal Acetals

Terminal acetals were selectively synthesized from various unbiased aliphatic terminal alkenes and 1,2-, 1,3-, or 1,4-diols using a PdCl₂(MeCN)₂/CuCl catalyst system in the presence of p-toluquinone under 1 atm of O₂ and mild reaction conditions. The slow addition of terminal alkenes suppressed the isomerization to internal alkenes successfully. Electron-deficient cyclic alkenes, such as p-toluquinone, were key additives to enhance the catalytic activity and the anti-Markovnikov selectivity. The halogen groups in the alkenes were found to operate as directing groups, suppressing isomerization and increasing the selectivity efficiently.

Asymmetric intramolecular aza-Michael reaction in desymmetrization processes. Total synthesis of hippodamine and epi-hippodamine

The use of chiral sulfinyl amines both as nucleophilic nitrogen sources and chiral inducers has been described for the first time in a desymmetrization-type process involving an intramolecular aza-Michael reaction. The resulting product was employed as an advanced intermediate in the total synthesis of the natural product hippodamine and epi-hippodamine, taking advantage of the special symmetry of these molecules. In addition, this is the first asymmetric total synthesis of epi-hippodamine.

Anomalous nuclear Overhauser effects in carbon-substituted aziridines: scalar cross-relaxation of the first kind

Anomalous NOESY cross-peaks that cannot be explained by dipolar cross-relaxation or chemical exchange are described for carbon-substituted aziridines. The origin of these is identified as scalar cross-relaxation of the first kind, as demonstrated by a complete theoretical description of this relaxation process and by computational simulation of the NOESY spectra. It is shown that this process relies on the stochastic modulation of J-coupling by conformational transitions, which in the case of aziridines arise from inversion at the nitrogen center. The observation of scalar cross-relaxation between protons does not appear to have been previously reported for NOESY spectra. Conventional analysis would have assigned the cross-peaks as being indicative of a chemical exchange process occurring between correlated spins, were it not for the fact that the pairs of nuclei displaying them cannot undergo such exchange.

Asymmetric synthesis of chloroisothreonine derivatives via syn-stereoselective Mannich-type additions across N-sulfinyl-α-chloroimines

Mannich-type reactions across N-sulfinyl-α-chloroaldimines resulted in syn-stereoselective synthesis of chloroisothreonine derivatives as excellent building blocks.

Stereocontrolled syntheses of (-)-cubebol and (-)-10-epicubebol involving intramolecular cyclopropanation of alpha-lithiated epoxides

Formylation of (-)-menthone (11) with LDA and HCO(2)CH(2)CF(3) avoids loss of configurational integrity at the isopropyl group, giving hydroxymethylenementhone 12. Lithium 2,2,6,6-tetramethylpiperidide-induced intramolecular cyclopropanation of derived unsaturated terminal epoxide 17 (and chlorohydrin 16), efficiently generates a substituted tricyclo[4.4.0.0(1,5)]decan-4-ol 18, which is used in a concise synthesis of (-)-cubebol (1). In contrast, isopropyl group inversion during formylation of menthone with NaOMe and HCO(2)Et led, by a similar strategy, to syntheses of 7-epicubebol (33) and (from (+)-menthone) of naturally occurring (-)-10-epicubebol (39), confirming the original structural assignment. Computational studies support the origin of the inversion as being rate-determining formylation of cis-enolate 27 from a mixture of rapidly interconverting enolates. In the synthesis of 7-epicubebol (33), allylic tertiary C-H insertion is observed as a significant competing reaction in the intramolecular cyclopropanation of unsaturated terminal epoxide 22.

Highly diastereoselective addition of alkynylmagnesium chlorides to N-tert-butanesulfinyl aldimines: a practical and general access to chiral alpha-branched amines

The addition of alkynylmagnesium chlorides to N-tert-butanesulfinyl imines proceeded with a remarkably high diastereoselectivity (dr > 13:1, mostly diastereopure), and with a general scope of both reaction partners. The high dr translated into simplified purification and higher optical purity for the synthesis of a wide array of chiral alpha-branched amines. The alkyne functionality also provides a multitude of opportunities for further synthetic transformations. The short asymmetric synthesis of (+)-angustureine 7 and (-)-cuspareine 10 was realized with use of this approach.

Highly stereoselective methylene transfers onto butanediacetal-protected chiral non-racemic sulfinyl imines using S-ylide technology

Diastereomeric ratios of >95 : 5 were obtained when performing methylene transfers onto imines originating from d-mannitol and (S)-(-)-2-methyl-2-propane sulfinamide or ascorbic acid and (R)-(-)-2-methyl-2-propane sulfinamide.

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).

Terminal aziridines by alpha-deprotonation/electrophile trapping of N-protected aziridine

N-tert-Butylsulfonyl and N-tert-butylsulfinyl aziridine undergo alpha-lithiation/electrophile trapping providing a new entry to terminal aziridines. With N-tert-butylsulfinyl aziridine complete asymmetric induction is observed alpha to nitrogen.