Ring Substitution Reactions Research Articles

Organic chemistry: an acid-base approach

Organic chemistry: an acid-base approach

Nucleophilic Ring-Substitution Reactions of Unsymmetrical Quadridentate Schiff Base and Its Complex of Nickel(II) or Copper(II) with Ethyl Mercaptoacetate

Abstract The nucleophilic replacement of halogen on the methine carbon of a Schiff base complex of nickel(II) or copper(II) by ethyl mercaptoacetate in dichloromethane proceeds via a four-centered intermediate, in which two polarizable atoms, such as bromine and sulfur, may stabilize strained bond angles. In the case of a free Schiff base ligand, a relatively stable adduct was spectrophotometrically confirmed. The adduct is thought to have a configuration analogous to that of a spiro compound containing a five-membered ring. Free ligands show no absorption bands in the wavelength region longer than 340 nm, while the adduct shows band at 375 nm assignable to a n-π* transition.

The nucleophilic ring substitutions of asymmetrical tetradentate schiff base complexes of nickel(II) and copper(II)

Seven new complexes where the chelate ring was nucleophilically substituted were synthesized by the reactions of asymmetrical tetradentate Schiff base complexes of nickel(II) and copper(II) with benzenethiols and thiolycollic ehtyl ester. They were characterized by means of elemental analyses, electronic and 1H-NMR spectra. Kinetics of the nucleophilic ring-substitution reactions were spectrophotometrically studied in a benzene solution. A four-centered intermediate is proposed for the reactions.

Reactions of phenols with tung oil

As regards the aromatic ring substitution reactions of various kinds of phenols with tung oil under acidic conditions, an investigation was made on the influences of the kinds and substitution positions of alkyl groups of the phenlos on the reaction. Alkyl phenols increased in reactivity in the order of ortho, meta, and para in the position of alkyl substitution. This can be attributed to the preferential para addition of tung oil to the phenol nucleus as reported in the previous paper. The larger alkyl group gave increased reactivities in the reactions of alkyl phenols with tung oil. This has something to do with compatibilities between phenols and tung oil (differences in solubility parameter between phenols and tung oil).

The competing methoxymercuration and ring-mercuration reactions of some alkylvinyl-substituted ferrocenes

Product analysis and kinetic data for the reaction of some alkylvinylferrocenes with mercuric acetate in methanol are reported. Depending on the location and nature of the alkyl group(s), exclusive addition or ring-substitution reactions are observed as well as both reactions together. This behaviour is interpreted in terms of the relative polar and steric effects. Styrene has also been investigated under similar conditions to provide comparisons of mechanistic significance. The methoxymercuration reaction seems to proceed via a slowly formed, possibly bridged intermediate, with weak carbonium ion character; with the ferrocene derivatives as substrates it appears to be a complex process as suggested by an anomalous temperature-dependence behavior.

Side-bonded ketone complexes of platinum(0). Indan-1,2,3-trione complexes; molecular and crystal structure of [2,2′,-bis(indan-1,2,3-trionato)(2–)-O2O2′]bis(triphenylphosphine)platinum

Reactions of equimolar quantities of [PtL4](L = PPh3 or AsPh3) with either indan-1,2,3-trione (int) or 2,2-di-hydroxyindan-1,3-dione afford the side-bonded ketone complexes [Pt(int)L2] which undergo ring-expansion reactions with int to give [Pt{(int)2}L2]. Crystals of the adduct [Pt{(int)2}(PPh3)2] are monoclinic, space group Cc with a= 22.08, b= 14.47, c= 30.72 Å, β= 95.1°, and Z= 8. Least-squares refinement of the structural parameters reduced R to 0.078 for 2 382 reflections. The adduct has the two indan-1,2,3-trione moieties linked via the carbon atoms of the central carbonyl groups and bonded by the oxygen atoms at these groups to the platinum to give a five-membered 1,3-dioxa-2-platinolan ring. Ring-expansion reactions of [Pt(int)L2] and ring-substitution reactions of [Pt{(int)2}L2], with hexafluoropropan-2-one and hexafluorobut-2-yne are also described. Reactions with hexafluoropropan-2-one give both five- and seven-membered ring systems. The side-bonded complexes [Pt(int)L2] react with dioxygen to give cyclic dicarboxylato-complexes.

Recent Synthetic Methods for Pyrroles and Pyrrolenines (2H- or 3H-Pyrroles)

The methods employed in the synthesis of monocyclic pyrroles and pyrrolenines (2H- and 3H-pyrroles) have been surveyed. The procedures have been classified according to the type of precursor used (cyclic or acyclic) in the production of the pyrrole system. 1. Pyrroles from Cyclic Precursors 1.1. Ring Substitution Reactions 1.2. Substituent Alteration Reactions 1.3. Elimination Reactions 1.4. Rearrangement Reactions 1.5. Ring Expansion Reactions 1.6. Ring Contraction Reactions 2. Pyrroles from Acyclic Precursors 2.1. Mucic Acid 2.2. Dicarbonyl Compounds 2.3. Acyloins 2.4. Unsaturated Compounds 2.5. Azines 2.6. Enamines 2.7. Amino Carbonyl Compounds or Precursors (Knorr Method) 2.8. Halo Carbonyl Compounds 3. Pyrrolenine (2H- and 3H-Pyrrole) Syntheses 3.1. Alkylation Methods 3.2. lsomerization Methods 3.3. Ring Closure Methods 3.4. Oxidative Methods 3.5. Miscellaneous Methods

Recent Advances in the Chemistry of Phenothiazines

This chapter discusses the chemistry of phenothiazines— that is, preparation of phenothiazines via ring closure, molecular structure and physical properties, free radicals, cations, and charge-transfer complexes within the phenothiazine class, ring substitution reactions of phenothiazines, and metabolism of phenothiazines. The name “phenothiazine” and the numbering given in the Revised Ring Index, used in Chemical Abstracts, and recommended by the lUPAC Rules of Organic Nomenclature is be used throughout this chapter. The 0- and p-quinonoid forms of phenothiazine— namely, 1H-, 3H-, and 4aH-phenothiazine are represented only by 3H-phenothiazines, in which both the hydrogen atoms are substituted. The cation obtained on two-electron oxidation of phenothiazine is referred to as the phenazathionium cation.

METALLOCENE CHEMISTRY—A DECADE OF PROGRESS

One of the most significant new frontiers in chemistry during the past decade has been the stabilization and study of π-organic derivatives of the transition metals. Over 60 elements are now known to form one or more cyclopentadienyl compounds. The aromatic-type reactions displayed by ferrocene and related complexes have also been extensively investigated. Ferrocene will undergo alkylation, acylation, sulphonation, metalation, arylation, formylation, aminomethylation, and other reactions characteristic of a highly reactive aromatic system. π-Cyclopentadienyl derivatives of vanadium, chromium, manganese, ruthenium, and osmium as well as certain π-arene complexes of chromium exhibit ring substitution reactions in varying degrees. Other metallocenes undergo ring addition reactions.The orientation effects of substituents on reactions of substituted ferrocenes have been studied. A variety of unique oxidation, reduction, dehydration, and rearrangement reactions are known in metallocene chemistry. Haloferrocenes and mercuriferrocenes are readily converted to biferrocenyl. Recent rate investigations have established that carbonium ions adjacent to metallocene nuclei possess unusual stabilization as a result of direct metal participation.