General description
N-Bromo Succinamide (NBS) is a popular bromination
reagent. It is a versatile source of bromine for reactions such
as electrophilic additions and radical substitution.
Advantages over other reagents:
The easy removal of Succinamide after bromination.
The possibility to fine tune its reactivity and properties via combination
with other reagents
It is therefore widely used in the synthesis of advanced fine chemical
intermediates, especially in the area of pharmaceuticals.
Applications:
1) Bromination in Allylic and Benzylic
positions:
NBS is widely known as its ability to brominate in Allylic
and benzlic positions if used in combination with a source of radicals.
- Apart from reacting selectively in Allylic positions, it shows
remarkable selectivity of Allylic methylene over Allylic methyl.
- In Benzylic brominations, no HBr is formed which makes in the
presence of HBr sensitive functional groups is required. The cleavage
of benzylidene acetals is a selective method to remove benzylidene
protection of vicinal diols and has found applications in the synthesis
of natural products, especially carbohydrates.
2) ά- Bromination of Carbonyl Derivatives:
Carbonyl derivatives can only be attacked if radical intermediates
are stabilized, for example by the captodative effect. According
to this principle. ά-amino acid derivatives can be ά-brominated.
3) Bromination of aromatic compounds:
Electron rich aromatic compounds can be brominated regioselectively.
4) Bromohydration and Bromolactonisaion:
The bromination of alkenes gives, 2-bromohydrines,
with selective attack on the most electron-rich double bond. Bromohydrines
can be transformed into a variety of useful derivates among them
epoxides. Initial attack of bromine to a double bond can be followed
by intramolecular attack giving rise to lactones, cyclic ethers
etc.
Combination
with other reagents:
The bromination properties of NBS can be fine-tuned
via combination with other reagents.
- NBS/HBr is used to convert acid chlorides into ά -bromo-acid
chlorides.
- Combination with nucleophiles: In the course of addition
to a double bond a variety of nucleophiles can be used: addition
of azide ions yields to bromo azides; addition of fluoride ions
yields to bromo fluorides.
- NBS/DMF is an effective blend for the selective monobromination
of electron-rich aromatic compounds.
- NBS/Dimethyl sulfide converts Allylic and Benzylic alcohols
into the corresponding bromides, even in the presence of sensitive
functional groups.
- The system can also be used to oxidize other, both for the
selective monobromination of electron-rich aromatic compounds.
- NBS/Dimethyl sulfide converts Allylic and Benzylic alcohols
into the corresponding bromides, even in the presence of sensitive
functional groups.
The system can also be used to oxidize other, both
primary and secondary alcohols, to the corresponding carbonyl compounds.
Handling:
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