Mukund P. Sibi

Radicals in organic synthesis

PART I: BASIC PRINCIPLES. Radical chain reactions. Single electron. Properties of radicals. Stereoselectivity of radical reactions. PART II: APPLICATIONS. Cascade reactions. Radical rearrangements. Miscellaneous applications. Radicals in total synthesis. Heteroatom centered radicals. Radicals in biomaterials.

Copper(II)-catalyzed exo and enantioselective cycloadditions of azomethine imines.

A strategy for exo and enantioselective 1,3-dipolar cycloaddition of azomethine imines to 2-acryloyl-3-pyrazolidinone is described. The corresponding cycloadducts are isolated with high diastereoselectivities (up to >96:4 exo/endo) and enantioselectivities (up to 98% ee).

Enantioselective Organo‐Photocatalysis Mediated by Atropisomeric Thiourea Derivatives

Can photocatalysis be performed without electron or energy transfer? To address this, organo-photocatalysts that are based on atropisomeric thioureas and display lower excited-state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4-alkenyl-substituted coumarins, which led to the corresponding products with high enantioselectivity (77-96% ee) at low catalyst loading (1-10 mol%). The photocatalytic cycle proceeds by energy sharing via the formation of both static and dynamic complexes (exciplex formation), which is aided by hydrogen bonding.

A new nucleophilic alaninol synthon from serine

Abstract A new nucleophilic alaninol synthon derived from serine is reported. The utility of this reagent in the stereoselective synthesis of β,γ-unsaturated amino alcohols is described.

Temperature dependent reversal of stereochemistry in enantioselective conjugate amine additions

Enoates derived from 4,4-disubstituted-2-oxazolidinones undergo enantioselective conjugate amine addition when mediated by a chiral Lewis acid derived from magnesium bromide and a bisoxazoline. The face selectivity in these amine additions is temperature dependent. They show an unusual reversal at two different temperatures.

Catalytic Kinetic Resolution of Biaryl Compounds.

Biaryl compounds with axial chirality are very common in synthetic chemistry, especially in catalysis. Axially chiral biaryls are important due to their biological activities and extensive applications in asymmetric catalysis. Thus the development of efficient enantioselective methods for their synthesis has attracted considerable attention. This Minireview discusses the progress made in catalytic kinetic resolution of biaryl compounds and chronicles significant advances made recently in catalytic kinetic resolution of biaryl scaffolds.

Fluxionally Chiral DMAP Catalysts: Kinetic Resolution of Axially Chiral Biaryl Compounds

Can organocatalysts that incorporate fluxional groups provide enhanced selectivity in asymmetric transformations? To address this issue, we have designed chiral 4-dimethylaminopyridine (DMAP) catalysts with fluxional chirality. These catalysts were found to be efficient in promoting the acylative kinetic resolution of secondary alcohols and axially chiral biaryl compounds with selectivity factors of up to 37 and 51, respectively.

Enantioselective intermolecular free radical conjugate additions. Application of a pyrazole template

Abstract An achiral pyrazole template has been evaluated in enantioselective conjugate radical additions. The enantioselectivity using the pyrazole template is inferior to those obtained from an oxazolidinone template. The two templates give products of opposite configuration using the same chiral Lewis acid.

Tin-Free Enantioselective Radical Reactions Using Silanes

Readily available hexyl silane is an excellent choice as a H-atom donor and a chain carrier in Lewis acid mediated enantioselective radical reactions. Conjugate radical additions to alpha,beta-unsaturated imides at room temperature proceed in good yields and excellent enantioselectivities.

Enantioselective radical reactions: the use of metal triflimides as Lewis acids

Abstract Several metal triflimides in conjunction with chiral ligands have been evaluated in conjugate radical additions. Chiral Lewis acids derived from magnesium and iron triflimides and bisoxazolines gave high enantioselectivity.