Marco Bella

Multiple Catalysis with Two Chiral Units: An Additional Dimension for Asymmetric Synthesis

This Minireview focuses on asymmetric reactions mediated by two distinct chiral catalysts (chiral multiple catalysis). Initially, this approach appears unconventional, but indeed it allows a fast multidimensional optimization and fine-tuning of the catalytic system required to perform a given transformation. Herein, this emerging concept is presented and its potential applications are highlighted.

Non-asymmetric organocatalysis

Asymmetric organocatalysis is now an established methodology for the preparation of chiral compounds. However, these are not the only valuable molecules which can be conveniently obtained. Organocatalytic reactions affording achiral compounds are gaining momentum, opening unexplored pathways in the synthesis of densely functionalized aromatic moieties, olefins and useful molecules such as natural substances.

Biomimetic Organocatalytic Asymmetric Synthesis of 2-Substituted Piperidine-Type Alkaloids and Their Analogues

Natural substances such as pelletierine and its analogues have been prepared in up to 97% ee and good yield by a protective-group-free, biomimetic approach. Usage of benzonitrile or acetonitrile as solvents effectively prevents product racemization.

Asymmetric carbolithiation of 2-phenylselenofumarate derivatives: a short synthesis of (−)-roccellaric acid

Abstract (−)-Roccellaric acid and variously substituted succinates are obtained through direct asymmetric carbolithiation of 2-phenylselenofumarate derivatives, followed by reaction with suitable electrophiles.

Quinine‐Catalyzed Asymmetric Synthesis of 2,2′‐Binaphthol‐Type Biaryls under Mild Reaction Conditions

Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non-C2 -symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity.

Direct amino-phenylselenylation of enoates: An easy route to α-phenylseleno-β-amino esters and β-lactams

Abstract A “one-pot” procedure to obtain α-phenylseleno-β-amino esters from the corresponding enoates is described. The target compounds are useful synthetic tools and direct precursors of new α-phenylseleno-β-lactams, which can be easily transformed into their α-alkylidene analogues. A direct procedure to obtain α-phenylseleno-β-amino esters from the corresponding enoates is described. The target compounds are direct precursors of new α-phenylseleno-β-lactams. Download : Download full-size image

Multicomponent asymmetric reactions mediated by proline lithium salt

The multicomponent reaction between proline lithium salt, 2-cyclohexen-1-one and aliphatic aldehydes affords the 4-alkylidene-2-cyclohexen-1-ones, which are interesting fragrances, and bicyclic amino acids that bear four additional stereocenters, obtained as single stereoisomer.

Direct vinylogous aldol addition of γ-butyrolactones and γ- butyrolactams

Abstract Deprotonation of N-benzyl-3-phenylselenylpyrrol-2(5H)-one 3 and furan-2(5H)-one 4 and reaction with aldehydes affords regioselectively 5-(1′-hydroxy)-γ-butyrolactones and the aza-analogous butyrolactams with good diastereoisomeric excesses. The presence of Lewis acids enhances the diastereoisomeric ratios. This methodology is an alternative to Lewis acid mediated silyloxydiene condensation.

3-Phenylselanylfuran-2(5H)-one: A versatile building block in the synthesis of lignans. A new approach towards 3,4-dibenzyl γ-butyrolactones

Abstract Ready available 3-phenylselanylfuran-2(5 H )-one undergoes tandem conjugate addition-alkylation by organocopper reagents to afford, with good yields and diastereoselectivities, 3,4-disubstituted-3-phenylselanyl-γ-butyrolactones, which can be transformed into naturally occurring compounds, such as lignans.

Efficient preparation of 3-substituted-furan-2(5H)-ones and their direct vinylogous aldol addition

Abstract The deprotonation of 3-substituted-furan-2(5H)-ones 1, obtained via the hydrolysis of 3-substituted-2,5-dihydro-2,5-dimethoxyfurans, affords in the reaction with both aromatic and aliphatic aldehydes regioselectively the unsaturated 3-substituted 5-(1′-hydroxy)-γ-butyrolactones, such as 4, 5, 6, 7, 8, 9 and 10. The use of Lewis acids allows modulation of the diastereoisomeric ratios. The subsequent reduction, carried out with nickel boride, gives rise to the formation of the corresponding saturated 5-(1′-hydroxy)-γ-butyrolactones, such as 11, 12 and 13.