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.

Methylation is one of the most fundamental synthetic transformationsi no rganic chemistry, but usually employs hazardous and toxicr eagents, such as methyl iodide,d imethyls ulfate,d iazomethane and dimethylc arbonate.I no rder to address sustainable development and green strategies,s ynthetic chemists have devoted much effort to the discovery and development of new methylating reagents,w hich are successfully beinga pplied in transition metal-catalyzed cross-coupling reactions.I nt his review,r ecent advances in this area are summarized, mainly including C-methylation, N-methylation and O-methylation.T he respective reaction mechanisms are also discussed. 1I ntroduction 2C -Methylation 2.1 Methylation of Aryl and Vinyl (Pseudo)Halides 2.2 Methylation of C À HB onds 2.3 Decarboxylative Methylation of a,b-Unsaturated Acids 2.4 Others 3N -Methylation of N-Containing Compounds 4O -MethylationofC arboxylic Acids 5C onclusions and Perspectives

The Rh-catalyzed, remote terminal hydroarylation of active olefins at the C7-position of indoles and the ortho-position of indolines and anilines with the appropriate choice of a N-P Bu directing group through long-range deconjugative isomerization has been reported. This transformation not only overcomes the conjugate rule of Michael acceptors but also controls the positional selectivity of indoles, representing a significant advancement in both alkene isomerization and the C-H alkylation of indoles.

N-Oxide compounds are very important intermediates in synthetic organic chemistry as well as in the chemical industry. Numerous efforts have been devoted to the development of efficient approaches for the C À H bond activation and functionalization of N-oxides in recent years, including arylation, alkenylation, alkylation, acyloxylation, amination, amidation and sulfonylation. In this review, recent advances in this area are summarized and their mechanisms are discussed.

Decarboxylative functionalization of α,β-unsaturated carboxylic acids is an emerging area that has been developed significantly in recent years. This critical review focuses on the different decarboxylative functionalization reactions of cinnamic acids leading to the formation of various C-C and C-heteroatom bonds. Apart from metal carboxylates, decarboxylation in cinnamic acids has been achieved efficiently under metal-free conditions, particularly via the use of hypervalent iodine reagents. We believe this review will encourage organic chemists to develop vinylic decarboxylation in a more appealing way with an understanding of new mechanistic insight.

Development of methodology for the preparation of nitroolefins is of significant interest to organic chemists. Recently, numerous useful methods have been developed, mainly including direct nitration of olefinic C-H bonds, nitro-decarboxylation of aromatic α,β-unsaturated carboxylic acids, ipso-nitration of vinylboronic acids and multidehydrogenative cross-coupling reaction of (hetero)arenes with nitroethane. This review will focus on recent achievements in nitroolefin synthesis and the mechanisms of the reactions are also discussed.

An exclusive catalytic C4-selective fluoroalkylation of indoles with highly active (1H, 1H-perfluoroalkyl)mesityliodonium triflate has been described. The key to its high regioselectivity is the appropriate choice of an easily accessible, cheap and removable directing group at the C3 position in the presence of a Pd(OAc) catalyst. Besides indole fluoroalkylation, the application of this strategy in other heteroarenes such as benzo[b]thiophene is also described.

An efficient protocol for silver/copper-cocatalyzed direct sulfenylation and selenylation of arenes with aryl disulfides and diselenides has been developed. This strategy exhibits excellent functional group tolerance and high regioselectivity. Mono sulfenylation and selenylation products can be exclusively achieved. This reaction provides a simple and practical route to the preparation of aryl sulfides and selenides.