Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Publisher Summary This chapter deals with reactions involving carbocationic transition states, in most cases forming intermediates having carbocationic centers at the conjugative position in the side chain. Yukawa–Tsuno (Y–T) introduced the concept of the varying resonance demand of reactions into substituent effect analysis. Nevertheless, the correlation results were always compared with those of the Brown equation implying constant resonance demand. The Y–T equation has been used extensively in studies of electrophilic substitution in the aromatic ring, and aliphatic nucleophilic substitution and related reactions forming a carbocation or a carbocationic (electron-deficient) center at the conjugative position (mostly benzylic position) in the side chain. The Y–T equation has proved to be one of the most fundamental and essential equations for understanding structure–reactivity relationships in chemical reactions using the language of the physical organic chemist.

The Yukawa-Tsuno Relationship in Carbocationic Systems

Publisher Summary This chapter discusses the experimental conditions, under which it is possible to obtain data relevant to the study of the bromination mechanism, and presents the evidence for the occurrence of charge transfer complexes and cationic intermediates on the reaction pathway. The chapter presents the kinetic substituent and solvent effects on this cation-forming halogenation; these effects are discussed in terms of kinetic selectivity, transition-state shifts and solvation. From an energetic point of view, free bromine addition can be considered as an ionization process leading from a neutral reagent to a cation-anion pair in a single elementary step, most work on this electrophilic addition can be used to understand how charge separation and stabilization occur in the organic reactions. Bromination thus appears as a suitable model, and is complementary to the conventional heterolytic substitutions. The association of kinetics and stereochemistry is particularly useful for obtaining data on the structure, open or bridged depending on the substituents of bromination intermediates.

Electrophilic Bromination of Carbon—Carbon Double Bonds: Structure, Solvent and Mechanism

Bromonium ions or .beta.-bromocarbocations in olefin bromination. A kinetic approach to product selectivities

Die grose Vielfalt organischer und metallorganischer Reaktionen kann bei Betrachtung aller Nucleophile und Elektrophile als Elektronendonoren (D) bzw. -acceptoren (A) mit einem vereinheitlichenden Mechanismus beschrieben werden. Der Vergleich von „outer-sphere”- und „inner-sphere”-Elektronenubertragungen mit Hilfe der Marcus-Theorie liefert die thermochemische Basis der „Verallgemeinerten Freien-Enthalpie-Beziehung fur die Elektronenubertragung” (generalized Free Energy Relationship for Electron Transfer, FE-RET) – siehe Gleichung (37) sowie die daraus folgenden Gleichungen (43) und (44) –, die auf elektrophile aromatische Substitutionen, Additionen an Olefine, Spaltungen von Alkyl-metallverbindungen etc. breit anwendbar ist. FERET basiert auf der Umwandlung der durch schwache Nucleophil-Elektrophil-Wechselwirkungen gekennzeichneten, allgegenwartigen Elektronen-Donor-Acceptor(EDA)-Vorlauferkomplexe [D, A] in Radikalionen-paare [D⊕, A−], wofur die Anderung der Freien Enthalpie nach der Mulliken-Theorie aus den Charge-Transfer-Absorptionsspektren abgeschatzt werden kann. Die FERET-Analyse last darauf schliesen, das die Charge-Transfer-Ionenpaare [D⊕, A⊖] den Ubergangszustanden von Nucleophil/Elektrophil-Umwandlungen energetisch aquivalent sind. Das Verhalten solcher Ionenpaare kann in einigen Fallen unmittelbar nach einem 25ps-Laserpuls auf die Charge-Transfer-Bande des EDA-Vorlauferkomplexes direkt beobachtet werden. Derartige Studien bestatigen beispielsweise das Radikalpaar [Aren⊙⊕, NO] als existenzfahiges Intermediat der elektrophilen Nitrierung von Arenen, wie anhand des Mechanismus der Elektronenubertragung von Arenen auf das Nitryl-Kation NO als Elektrophil beschrieben wird.

Elektronen- und Ladungsübertragung: Zur Vereinheitlichung der mechanismen organischer und metallorganischer Reaktionen

Ethylenic compounds reactivity: bromination—XLI1: Relative reactivities of R1CMeCH2 and R1CHCMe2 series as a criterion for distinguishing between bridged and acyclic transition states. Degree of symmetry of the bromonium ion-like transition state

Elisabeth Bienvenue-Goetz

Papers

Ethylenic compounds reactivity: bromination—XLI1: Relative reactivities of R1CMeCH2 and R1CHCMe2 series as a criterion for distinguishing between bridged and acyclic transition states. Degree of symmetry of the bromonium ion-like transition state

Substituent dependence of the selectivity in alkene bromination through bromocarbenium ions

The polar reaction constant for alkene chlorination. similarity and differences in the chloronium and bromonium ion like transition states.