Glycomimetics versus multivalent glycoconjugates for the design of high affinity lectin ligands.

Unsaturated nitriles: conjugate additions of carbon nucleophiles to a recalcitrant class of acceptors.

Enamines: recent advances in synthetic, spectroscopic, mechanistic, and stereochemical aspects—I

Stereoelectronic factors account for the apparent reversal of donor–acceptor properties of a variety of functional groups by a simple change of their orientation in space. The new reactivity patterns that arise from spatial anisotropy are associated with chameleonic behavior of common organic functionalities.

Stereoelectronic Chameleons: The Donor-Acceptor Dichotomy of Functional Groups.

On the Steric Course of the Reaction of Enamines Derived from Open-Chain Aldehydes and Ketones with Nitro-olefins Yielding 2,3-Disubstituted 4-Nitroketones



The relative configuration of the nitro-ketone 12 obtained by the title reaction has been proved by a Baeyer-Villiger degradation and subsequent reduction to the amino-alcohol (±)-(u)-20, the relative configuration of which is identical with a sample prepared from 2-methyl-3-hydroxybutyrate of known configuration (Scheme 1). The stereochemical course of the title reaction is thus as predicted by our topological rule. It is assumed that the other nitro-ketones 13–18 described here are also formed by (lk)-combination of the trigonal centers of the educts (diastereoselectivity > 90%, see Formulae and Fig. 1). It is not possible to reverse this relative topicity by employing (Z)- instead of (E)-components of the starting materials, due to the reversibility of the primary step of these Michael additions (Schemes 2 and 3, and Fig. 2).

Über den sterischen Verlauf der Umsetzung von Enaminen aus offenkettigen Aldehyden und Ketonen mit Nitroolefinen zu 2,3‐disubstituierten 4‐Nitroketonen

The 13C chemical shifts of a series of acyclic enamines derived from morpholine and pyrrolidine are reported. There is considerable variation in the contribution of the amine moiety to the chemical shift of the olefinic C-2, which is attributed principally to variation in the mesomeric contribution to the electron density. The amine contribution to the chemical shift of the olefinic C-1 is relatively constant if allowance is made for changes in the shift parameters of the alkyl substituents.

Enamine chemistry. Part 22. Carbon-13 nuclear magnetic resonance spectra of acyclic enamines

Enamines derived from isoxazolidine and 1,3-dioxa-5-azacyclohexane have been prepared. The effect of the addition a α- or β-heteroatoms is to decrease the pπ-conjugation between the nitrogen lone pair of electrons and the π-electrons of the double bond, as reflected in the spectral properties of the enamines and their reactivity with electrophiles. The reasons for this are discussed.

Enamine chemistry. Part 27. The effect of additional α- and β-heteroatoms on the pπ-conjugation and reactivity of enamines. Sub or super-enamines

The preparation and 13C chemical shifts of a series of N-alkyl-morpholines and -pyrrolidines are reported. The α-and β-effects of the amine moieties have been evaluated and compared with those operating in the corresponding enamines and with the α- and β-effects of an isopropyl group. The factors affecting the relative magnitude of these effects are discussed.

Enamine chemistry. Part 25. Preparation and carbon-13 nuclear magnetic resonance spectra of N-alkyl-morpholines and -pyrrolidines. Comparison with the carbon-13 spectra of the corresponding acyclic enamines

Reaction of [Fe(CO)5] and the morpholine and pyrrolidine dienamines of 3,5,5-trimethylcyclohex-2-en-1-one gives a mixture of two tricarbonyl(dienamine)iron complexes. The complex in which the dienamine system is cross-conjugated has been shown to be more stable than that in which the dienamine is linearly conjugated. The reason for this, and the effect on the spectral properties, are discussed.

Md. Giasuddin Ahmed

Papers

Enamine chemistry. Part 22. Carbon-13 nuclear magnetic resonance spectra of acyclic enamines

Enamine chemistry. Part 27. The effect of additional α- and β-heteroatoms on the pπ-conjugation and reactivity of enamines. Sub or super-enamines

Enamine chemistry. Part 25. Preparation and carbon-13 nuclear magnetic resonance spectra of N-alkyl-morpholines and -pyrrolidines. Comparison with the carbon-13 spectra of the corresponding acyclic enamines

Enamine chemistry. Part 23. Synthesis, spectral properties, and relative stabilities of cyclic dienamine complexes of tricarbonyliron

Enamine chemistry. part 23. synthesis, spectral properties, and relative stabilities of cyclic dienamine complexes of tricarbonyliron