Alpine borane

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.

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
  • InChI=1S/C18H31B/c1-12-16-10-13(18(16,2)3)11-17(12)19-14-6-4-7-15(19)9-5-8-14/h12-17H,4-11H2,1-3H3/t12-,13-,14?,15?,16+,17-/m1/s1 checkY
    Key: VCDGSBJCRYTLNU-AZWGFFAPSA-N checkY
  • InChI=1/C18H31B/c1-12-16-10-13(18(16,2)3)11-17(12)19-14-6-4-7-15(19)9-5-8-14/h12-17H,4-11H2,1-3H3/t12-,13-,14?,15?,16+,17-/m1/s1
    Key: VCDGSBJCRYTLNU-AZWGFFAPBY
  • CC4(C)[C@@H]1C[C@H]4[C@@H](C)[C@@H](C1)B3C2CCCC3CCC2
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
GHS labelling:
GHS02: Flammable
Danger
H250
P210, P222, P280, P302+P334, P370+P378, P422
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

Preparation and reactions

This reagent is generated by treating 9-BBN with α-pinene.[2]

This sterically crowded chiral trialkylborane can stereoselectively reduce aldehydes in what is known as the Midland Alpine borane reduction, or simply the Midland reduction.[3]

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.[4]

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.[2]

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. M. Midland (1989). "Asymmetric reductions with organoborane reagents". Chemical Reviews. 89 (7): 1553–1561. doi:10.1021/cr00097a010.
  3. 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
  4. Midland, M. Mark; Graham, Richard S. (1985). "Asymmetric Reduction of α,β-Acetylenic Ketones with B-3-Pinanyl-9-Borabicyclo[3.3.1]nonane: (R)-(+)-1-Octyln-3-ol". 63: 57. doi:10.15227/orgsyn.063.0057. {{cite journal}}: Cite journal requires |journal= (help)
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