Yu. G. Bundel

Organomelemental fragmentations : I. Direct and retro fragmentations in organometallic benzyl compounds. Aromatisational metallation

Abstract Organometallic benzyl compounds are known to react with eletrophilic agents via two paths, viz., by direct substitution of the metal by the agent, and by attack of the ortho - and para -positions of the ring. The latter reaction leads to expulsion of the metal and formation of unstable triene intermediates (1-methylene-2,4-cyclohexadienes and 1-methylene-2,5-cyclohexadienes). By attributing these processes to electrophilic fragmentations (referred to as F E ) a new process may be predicted to occur, electrpohilic addition of metal salts to the exo -methylene site of trienes of this type. This process can be regarded as the reverse of the fragmentation reaction. The F E representation proposed here forms the basis for a new organometallic synthesis, aromatisational metallation. It is shown that interaction of 1-methylene-6-ethyl-2,4-cyclohexadiene and 1-methylene-4-ethyl-2,5-cyclohexadiene with mercury dichloride in ether results in the formation of o - and p -ethylbenzylmercury chlorides, respectively.

Synthesis of hydroxyisoxazolidines on adsorbents

Abstract 3- And 5-hydroxyisoxazolidines can be synthesized in solution and on the surface of an adsorbent. The regioselectivity depends on the type of adsorbent used.

σ,π-conjugation and 199Hg shielding constants in benzyl derivatives of mercury

Abstract The 199 Hg chemical shifts in a number of benzylmercuric chlorides containing methyl substituents in various positions of the benzene nucleus are studied by the heteronuclear 1 H-{ 199 Hg} double resonance technique. Meta - and para -methyl substituents are shown to have no pronounced action on the shielding whereas ortho -methyl groups each shift the signal by 30 ppm downfield. The observed effect is due to an increase in the population of conformers with the CHg bond lying out of the aromatic cycle plane. The departure from planarity favours conjugation between the electrons of the CHg bond and the π-electronic system of the ring. The J ( 1 H 199 Hg) and J ( 13 C 199 Hg) coupling constant values obtained in this work confirm the latter conclusion.

Organoelemental fragmentations : III. On the mechanism of isotope enrichment of the aromatic ring in organometallic benzyl compounds when reacted with acids☆☆☆

Abstract The β-effect of a metal is mainly exhibited in decomposition of a metal—carbon bond. Nevertheless, there is a well known case in which it was assumed that the metal—carbon bond was retained in the course of electron delocalisation at the adjacent carbocation site. This reaction is isotopically labelled acid cleavage of benzylmercuric chloride, which results in both electrophilic fragmentation (F E ), leading to the 1-methylene-6-deuteriocyclohexadiene-2,4 intermediate, and in hydrogen/deuterium replacement, leading to isotope enrichment of the aromatic ring of the starting species. However, we found that this process is governed by an electrophilic fragmentation, not an electrophilic aromatic substitution, mechanism. The study of deuterio-demetalation of benzylmercuric chloride with deuterium chloride, containing a mercuric chloride additive, has revealed that the demetalation rate and the isotope enrichment rate are markedly dependent on the mercuric chloride concentration in the system. These results, inexplicable in terms of the CHg hyperconjugation concept (σ—π conjugation), may suggest that the metal—carbon bond conservation in the process under discussion is only apparent. A new two-step mechanism has been formulated for the reaction under study, based on aromatisational metalation of the exo -methylene—cyclohexadiene structures, leading to isotopically labelled benzyl organometallics under the action of metal salts.

The Use of Microwave Activation in the Chemistry of Heterocyclic Compounds. (Review)

Published data on the successful application of microwave activation in the chemistry of various heterocycles over the last two years are discussed.

Synthesis of O-vinyl ethers of 3-acylindole oximes and their heterocyclization to pyrrolylindoles

O-vinyl ether of 3-acylindole oximes have been synthesized and the possibility has been shown of their thermal conversion into pyrrolylindoles, which permits a heterocyclization mechanism including the stage of [3,3]-sigmatropic shift to be suggested.

Synthesis of isomeric O-(phenylvinyl)-acetophenone oximes and their rearrangement to pyrroles

Methods were developed for the radioselective synthesis of α- and β-O-(phenylvinyl)-acetophenone oximes. Their conversion to 2,5- and 2,4-diphenylpyrroles, respectively, confirms the mechanism of this process, including a step of [3,3]-sigmatropic displacement.

Organoelemental Fragmentations : II. A proof of tautomeric arene intermediates in reactions of organometallic benzyl compounds with acids. Aromatisational mercuration of 1-methylene-2,4-cyclohexadiene☆

Abstract Soft Lewis acids of the HgCl 2 type are effective electrophilic traps for tautomeric arenes even in strongly acidic media which catalyse aromatisation of the arenes. Acid cleavage of (PhCH 2 ) 3 SnCl by the action of DCl and HgCl 2 has been studied, and it is shown that the organotin compound is protolysed via a fragmentation mechanism involving a 1-methylene-6-deuterio-2,4-cyclohexadiene intermediate that yields o -D-C 6 H 4 CH 2 HgCl under the action of HgCl 2 .

Synthesis of isoxazolidine derivatives from N-substituted hydroxylamines and α,Β-unsaturated ketones

The reaction of methyl vinyl ketone with N-Phenyl-hydroxylamine leads to a tautomeric mixture of 5-hydroxy-2-phenyl-5-methylisoxazolidine and its linear form, while the reaction with benzohydroxamic acid leads to linear products of addition to the oxygen or nitrogen atoms, depending on the reaction conditions. The first representatives of 5-hydroxyisoxazolidines with the residue of an aliphatic carboxylic acid attached to the nitrogen atom were obtained by acylation of 5-hydroxy-3,3,5-trimethylisoxazolidine.

Synthesis and structure of hydroxyisoxazolidines and derivatives of hydroxylamine and alkenals

The reactions of N-substituted hydroxylamines with alkenals serve as a method for the synthesis of the corresponding 2-substituted 3(5)-hydroxyisoxazolidines. The reaction pathway is determined by the nature of the substituent attached to the nitrogen atom. Ring-chain isomerism has been detected in these newly obtained compounds