Alpine borane is the commercial name for an
organoboron compound that is used in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
. It is a colorless liquid, although it is usually encountered as a solution.
Preparation and reactions
This
reagent
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
is generated by treating
9-BBN with
α-pinene.
This sterically crowded
chiral trialkylborane can
stereoselectively reduce aldehydes in what is known as the
Midland Alpine borane reduction, or simply the Midland reduction.
:C
8H
12B-pinanyl + RCDO → C
8H
12BOCHDR + (+)-''d''-pinene
Hydrolysis of the resulting borinic ester affords the alcohol:
:C
8H
12BOCHDR + H
2O → C
8H
12BOH + HOCHDR
It is also effective for the stereoselective reduction of certain acetylenic ketones.
The reaction is proposed to involve formation of an adduct by coordination of the carbonyl oxygen to boron. Intramolecular hydride transfer from the pinane substituent to the carbonyl carbon ensues.
[
]
Related reagents
A range of alkyl-substituted borane are specialty reagents in organic synthesis. Two such reagents that are closely related to Alpine borane are 9-BBN and diisopinocampheylborane.
References
{{Reflist
Organoboranes
Reducing agents