Stephan Stanchev

Synthesis, absolute configuration and circular dichroism of some diarylmethane derivatives

Abstract Synthesis and assignment of the absolute configuration of different types of compounds bearing the diarylmethane moiety is presented. The absolute configuration was determined using chemical correlation and CD approaches based on the sign of the 0-0 vibronic transition within the α-aromatic ( 1 L b ) band of the substituted phenyl chromophore.

Unexpected change of absolute configuration in asymmetric Michael addition of methyl vinyl ketone to 2-nitrocycloalkanones

Abstract Michael addition of methyl vinyl ketone 2 to 2-nitrocycloalkanones 1 catalyzed by the Cinchona alkaloid cinchonine 3 affords adducts in high chemical yields in up to 60% enantiomeric excess. The configuration of the products depends on the ring size. Absolute configuration of (−)-2-nitro-2-(3-oxobutyl)cyclooctanone and (+)-2-nitro-2-(3-oxobutyl)cyclododecanone derivatives were determined by X-ray diffraction.

A short synthesis of 15-pentadecanolide

Abstract 15-Pentadecanolide was synthesised by a five step, two pot reaction sequence, starting from 2-nitrocyclododecanone in a 60% overall yield.

A route to optically active benzyl ester of (1-methyl-2-pyrrolidinyl)-acetic acid, an intermediate in the synthesis of Clemastine

Abstract A short and efficient synthesis of the title compound based on racemate resolution is described.

STEREOCHEMISTRY OF THE ADDITION OF METALLATED SULFONAMIDES TO SUBSTITUTED CYCLOHEXANONES

Abstract The addition of α-metallated sulfonamides to cyclic ketones has been studied. Under kinetic control the axial attack of the lithium and the cerium reagents to 4-tert-butylcyclohexanone is preferred, whereas the stereochemical result is inverse when the metal is iron. High regio- and stereoselectivity of the addition of lithiated sulfonamides to (-)-trans-menthone (3) and (+)-(R)-pulegone (4) was observed, namely only 1,2-addition occurs affording the axial (with 3) and equatorial (with 4) hydroxysulfonamides 7 and 10, resp. The reaction of phenylmethanesulfonamide reagents with 4 proceeds in 1,4 fashion. The configurations of the hydroxysulfonamides were established on the basis of NMR and X-ray analyses.

Absolute Configuration of a Substituted Cyclohexanol

The low-temperature X-ray structure of 1-(N,N-dimethylsulfamoylmethyl)-2-isopropyl-5-methyl-cyclohexan-1-ol, C 13 H 27 NO 3 S [alternative IUPAC name : 1-hydroxy-2-isopropyl-5,N,N-trimethylcyclohexane-methanesulfonamide], is reported. There are two molecules in the asymmetric unit. The absolute configuration has been determined.

Addition of Lithium Reagents of N,N-Dialkylsulfonamides to Mannich Bases

Abstract The addition of metallated N,N-dialkyl-sulfonamides 1 to Mannich bases 2, leading to N,N-dialkylamides of 4-(N′,N′-dialkylamino)-2-hydroxy-2-phenylbutanesulfonic acids (4) is described.