Asymmetric aza-Michael addition: synthesis of (−)-allosedridine and (−)-2-epi-ethylnorlobelol

Tandem One-Pot Biocatalytic Oxidation and Wittig Reaction in Water

We explore biocatalytic aldehyde generation under aqueous conditions, concomitantly delivering access to a one-pot Wittig reaction using stabilized phosphoranes and granting diverse alkene products. Using a recombinant choline oxidase mutant, we first undertake biocatalytic alcohol oxidation across a range of functional aliphatic primary alcohols, demonstrating a remarkable substrate tolerance for this enzyme, including chloride, bromide, azide, S-methyl, and alkynyl groups. Following this, we extend capability and deliver a practicable milligram-scale one-pot Wittig reaction in water.

O2 -Assisted Four-Component Reaction of Vinyl Magnesium Bromide with Chiral N-tert-Butanesulfinyl Imines To Form syn-1,3-Amino Alcohols

An O₂ -assisted, four-component reaction has been developed to synthesize a wide range of syn-1,3-amino alcohols in one step. The reaction proceeds by oxygenation of vinyl magnesium bromide (component-I) with O₂ (component-II) to give a magnesium enolate of acetaldehyde, which undergoes addition to a chiral N-tert-butanesulfinyl imine (component-III) followed by a sequential addition with excess vinyl magnesium bromide (component-IV). The approach allows diastereoselective synthesis of anti/syn- and syn/syn-3-amino-1,5-diols in good yields with high diastereoselectivity. The method was illustrated in an efficient, four-step synthesis of piperidine alkaloid (-)-2'-epi-ethylnorlobelol.

Recent advances in the asymmetric synthesis of pharmacology-relevant nitrogen heterocycles via stereoselective aza-Michael reactions

In this review, recent applications of a stereoselective aza-Michael reaction for asymmetric synthesis of naturally occurring N-containing heterocyclic scaffolds and their usefulness to pharmacology are summarized.

Mannich-type Reactions of Cyclic Nitrones: Effective Methods for the Enantioselective Synthesis of Piperidine-containing Alkaloids

Even though there are dozens of biologically active 2-substituted and 2,6-disubstituted piperidines, only a limited number of approaches exist for their synthesis. Herein is described two Mannich-type additions to nitrones, one using β-ketoacids under catalyst-free conditions and another using methyl ketones in the presence of chiral thioureas, which can generate a broad array of such 2-substituted materials, as well as other ring variants, in the form of β-N-hydroxy-aminoketones. Both processes have broad scope, with the latter providing products with high enantioselectivity (up to 98 %). The combination of these methods, along with other critical steps, has enabled 8-step total syntheses of the 2,6-disubstituted piperidine alkaloids (-)-lobeline and (-)-sedinone.

Direct asymmetric syntheses of chiral aldehydes and ketones via N-acyl chiral auxiliary derivatives including chiral Weinreb amide equivalents

This article covers N-acyl chiral auxiliary-based approaches to the asymmetric synthesis of enantiopure aldehydes and ketones. The use of diastereoisomerically pure N-acyl derivatives of chiral auxiliaries (including chiral Weinreb amide equivalents) and their conversion to the corresponding enantiopure aldehydes and ketones in a single synthetic operation by treatment with a hydride reducing agent or an organometallic reagent, respectively, are highlighted.

Total synthesis of sedum alkaloids via catalyst controlled aza-Cope rearrangement and hydroformylation with formaldehyde

The catalytic asymmetric aminoallylation of chiral aldehydes is developed as a new method for the catalyst controlled synthesis of syn- and anti-1,3-aminoalcohols. This methodology is highlighted in the synthesis of the sedum alkaloids (+)-sedridine and (+)-allosedridine both of which have their final carbon incorporated during closure of the piperidine ring via a hydroformylation with formaldehyde.