The stereochemistry of hippurate alkylation

Article Abstract:

Alkylation with benzyl bromide of the hippurate esters of trans 2-(p-substituted phenyl) cyclohexanol gives a high yield of phenylalanine derivatives. Stereoselectivity is in the range of 20% to more than 98%, values dependent on the aromatic group in the chiral cyclohexyl auxiliary. The sense of the induction can be predicted using a proposed model. Pi-stacking and interesting electronic effects related to alteration of a stereochemical result based on an aromatic residue apparently remote from the reacting center have been studied.

Conformational analysis, Alkylation, Alkylation (Petroleum refining)

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Stereoelectronic effects in sulfonyl compounds: axial orientation of an N-methyl group in a six-membered sultam

Article Abstract:

Stereoelectronic effects that exist in sulfonyl compounds are explored in a study of the axial orientation of an N-methyl group in a six-membered sultam. The axial orientation of the N-methyl group was shown by the single-crystal X-ray structure. The stereoelectronic effect could be part of the category 'generalized anomeric effects' or 'negative, or anionic, hyperconjugation.' A sulfonamide displaying competition between steric and stereoelectronic effects was synthesized and studied.

Analysis, X-ray crystallography, Amides

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Influence des ultrasons sur la diastereoselectivite; synthese d'imidazolidine-4-one chirales

Article Abstract:

Synthesis of imidazolidine-4-one has been carried out in three steps. An efficient reagent for the last step, reduction of a ketone, was sodium dithionite. The diastereoselectivity of the reaction is low, and at normal temperatures the reaction is slow. With ultrasound, selectivity and yield are quite good. With sodium dithionite this reaction can be carried out in water without hydrides. The article text is in French.

Ultrasonics

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