Christophe Allais

Generation of Stereochemically Defined Tetrasubstituted Enolborinates by 1,4‐Hydroboration of α,β‐Unsaturated Morpholine Carboxamides with (Diisopinocampheyl)borane

On all fours: The title reaction with (Ipc)2 BH provides tetrasubstituted enolborinates which undergo aldol reactions with aldehydes to form products with all-carbon quaternary centers with exceptional diastereo- and enantioselectivity. A change to the substitution pattern of the starting amide leads to either diastereomer of the α-methyl-α-ethyl-β-hydroxy carboxamide (1 or 2).

Diisopinocampheylborane‐Mediated Reductive Aldol Reactions: Highly Enantio‐ and Diastereoselective Synthesis of syn Aldols from N‐Acryloylmorpholine

An efficient and highly enantio- and diastereoselective synthesis of syn propionamide aldols is described. Formation of the Z-enolborinate via the hydroboration of 4-acryloylmorpholine with (diisopinocampheyl)borane followed by aldol reactions with representative achiral and chiral aldehydes provided syn-α-methyl-β-hydroxy morpholine carboxamides with excellent enantio- and diastereoselectivity (96–98% ee and d.r. >20:1).

Access to Highly Substituted 7-Azaindoles from 2-Fluoropyridines via 7-Azaindoline Intermediates.

A versatile synthesis of 7-azaindoles from substituted 2-fluoropyridines is described. C3-metalation and 1,4-addition to nitroolefins provide substituted 2-fluoro-3-(2-nitroethyl)pyridines. A facile oxidative Nef reaction/reductive amination/intramolecular SNAr sequence furnishes 7-azaindolines. Finally, optional regioselective electrophilic C5-substitution (e.g., bromination or nitration) and subsequent in situ oxidation delivers highly functionalized 7-azaindoles in high overall efficiency.

(Diisopinocampheyl)borane-mediated reductive aldol reactions of acrylate esters: enantioselective synthesis of anti-aldols.

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-α-methyl-β-hydroxy esters 9 or 10 with excellent diastereo- (up to ≥20:1 dr) and enantioselectivity (up to 87% ee). The results of double asymmetric reactions of 5E with several chiral aldehydes are also presented.

Enantio- and Diastereoselective Synthesis of 1,5-syn-(Z)-Amino Alcohols via Imine Double Allylboration: Synthesis of trans-1,2,3,6-Tetrahydropyridines and Total Synthesis of Andrachcine

A stereoselective synthesis of trans-1,2,3,6-tetrahydropyridines 8 is described. This synthesis proceeds via intramolecular Mistunobu reactions of 1,5-syn-(Z)-amino alcohols 7, which were prepared by a highly diastereo- and enantioselective double-allylboration reaction of aldehyde 5 and silylimine 6. The chiral bifunctional γ-borylallylborane 9E was generated in situ by hydroboration of allene 3 with (diisopinocampheyl)borane 4. This strategy was applied to the total synthesis of andrachcine 1, thus establishing with certainty the absolute and relative configuration of the natural product.