Alpine borane

Alpine borane[1]
Skeletal formula of alpine borane
Ball-and-stick model of the alpine borane molecule
Names
IUPAC name
9-(2,6,6-Trimethylbicyclo[3.1.1]hept-3-yl)-9-bora-bicyclo[3.3.1]nonane
Other names
Alpine-Borane; B-Isopinocampheyl-9-borabicyclo[3.3.1]nonane; B-3-Pinanyl-9-borabicyclo[3.3.1]nonane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.157.575
Properties
C18H31B
Molar mass 258.26 g·mol−1
Appearance Colorless liquid
Density 0.947 g/mL
Boiling point > 55 °C (131 °F; 328 K)
Hazards
F
R-phrases (outdated) R17
S-phrases (outdated) S6 S16 S24 S36/37/39
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Alpine borane is the commercial name for an organoboron compound that is used in organic synthesis. It is a colorless liquid, although it is usually encountered as a solution.

Preparation and reactions

This reagent is generated by treating 9-BBN with α-pinene.

This sterically crowded chiral trialkylborane can stereoselectively reduce ketones, aldehydes, even deutero aldehydes in what is known as the Midland Alpine Borane Reduction, or simply the Midland Reduction:[2]

C8H12B-pinanyl + RCDO → C8H12BOCHDR + (+)-d-pinene

Hydrolysis of the resulting borinic ester affords the alcohol:

C8H12BOCHDR + H2O → C8H12BOH + HOCHDR

It is also effective for the stereoselective reduction of certain acetylenic ketones.[3]

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

  1. R-Alpine-Borane and S-Alpine-Borane at Sigma-Aldrich
  2. M. Mark Midland "B-3-Pinanyl-9-borabicyclo[3.3.1]nonane" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley, New York.doi:10.1002/047084289X.rp173. Article Online Posting Date: April 15, 2001
  3. M. Mark Midland and Richard S. Graham. "Asymmetric Reduction of α,β-Acetylenic Ketones with B-3-Pinanyl-9-Borabicyclo[3.3.1]nonane: (R)-(+)-1-Octyln-3-ol". Org. Synth.; Coll. Vol., 7, p. 402
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