Synthesis of (E)-diethyl 6,6′-(diazene-1,2-diyl)bis(5-cyano-2-methyl-4-phenylnicotinates), a new type of 2,2′-azopyridine dyes

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

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.

The reaction of 2-amino-4H-pyrans with N-bromosuccinimide

The reaction of racemic 2-amino-4H-pyrans, such as 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles, with N-bromosuccinimide (NBS), in CH2Cl2, at room temperature, is a very quick, regio, stereoselective, and high yielding process, affording major racemic (1S, 2S)-2-bromo-3-imino-benzo[f]chromene or racemic (1S, 2S)-2-bromo-3-(bromoimino)-benzo[f]chromene derivatives, when using 1.0 or 2.2 equivalents of NBS, respectively. This reaction, extended to isomeric 2-amino-4-aryl-4H-benzo[h]chromene-3-carbonitriles, showed an unexpected reactivity, affording racemic (3S,4S)-3-bromo-2-(bromoimino)-benzo[h]chromene-3-carbonitriles or 2-oxo-2H-benzo[h]chromene-3-carbonitriles, when using 2.2 or 1.0 equivalents of NBS, respectively. The reaction of alkyl 6-amino-5-cyano-2-methyl-4H-pyran-3-carboxylates has yielded unstable racemic (3S,4S)-alkyl 3-bromo-2-(bromoimino)-3-cyano-6-methyl-3,4-dihydro-2H-pyran-5-carboxylates. The mechanism of these reactions has been investigated by computational methods.