Diisopinocampheylborane

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Diisopinocampheylborane

Structure of (+)-Diisopinocampheylborane dimer
Names
IUPAC name
Di[(1S,2R,3S,5S)-pinan-3-yl]borane
Systematic IUPAC name
Bis[(1S,2S,3S,5R)-2,6,6-trimethylbicyclo[3.1.1]heptan-3-yl]borane
Other names
(+)-Di-3-pinanylborane; Diisopinocampheylborane; Ipc2BH dimer
Identifiers
3D model (
JSmol
)
Abbreviations Ipc2BH
ChemSpider
  • InChI=1S/C20H35B/c1-11-15-7-13(19(15,3)4)9-17(11)21-18-10-14-8-16(12(18)2)20(14,5)6/h11-18,21H,7-10H2,1-6H3
    Key: KBGJOMVTAXYPAG-UHFFFAOYSA-N
  • InChI=1/C20H35B/c1-11-15-7-13(19(15,3)4)9-17(11)21-18-10-14-8-16(12(18)2)20(14,5)6/h11-18,21H,7-10H2,1-6H3
    Key: KBGJOMVTAXYPAG-UHFFFAOYAB
  • [H]B(C1CC2CC(C1(C))C2(C)(C))C3CC4CC(C3(C))C4(C)(C)
Properties
C20H35B
Molar mass 286.31 g·mol−1
Appearance Colorless solid
Density 1.044 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Diisopinocampheylborane is an

dimeric with B-H-B bridges.[1]

Preparation

Diisopinocampheylborane was originally prepared by hydroboration of excess α-pinene with borane,[2] but it is now more commonly generated from

borane-methyl sulfide (BMS).[3]

The compound can be isolated as a solid, but because it is quite sensitive to water and air, it is often generated in situ and used as a solution. The synthesis is complicated by a number of factors, including the tendency of the compound to eliminate pinene.[1]

Diisopinocampheylborane is often represented as a monomer (including in this article), but X-ray crystallography establishes a dimeric structure.[1]

Reactions

Oxidation of diisopinocampheylborane with basic hydrogen peroxide gives isopincampheol. Methanolysis gives methoxydiisopinocampheylborane

Hydroboration

Because of the large

2-pentene, 3-hexene are converted to the respective chiral alcohols in high ee's.[4] Norbornene under the same conditions gave an 83% ee. Heterocycles (dihydrofuran, dihydrothiophene, dihydropyrrole, tetrahydropyran) give the alcohols in ≥99% ee; the high ee's reflect their constrained conformations.[5]

It adds to alkynes to form the corresponding vinyldiisopinocampheylboranes

In a highly

aldehydes to the homologated alcohols, rapidly even at -100 °C.[6] The alkyldiisopinocampheylboranes, which result from the addition to alkenes, usefully react with a range of different reagents. Hydroxylamine-O-sulfonic acid provides 3-pinanamine.[7]

Also useful is the reaction of diisopinocampheylborane with an

boronic ester, (isopinocampheyl)2BOCH2(R), which can be further used is a number of reactions e.g. Suzuki reaction.[4]

Related campheylboranes

Diisopinocampheylchloroborane
Alpine borane

Treatment of diisopinocampheylborane with

ketones
:

In the above mechanism where G=O and R is Ipc and Cl or

aryl alkyl ketones and tert-butyl alkyl ketones. Diisopinocampheylchloroborane is often complementary with diisopinocampheylborane, where one provides the R enantiomer and the other the S, the enantioselectivity is typically very high.[9][10]

Alpine-borane is produced by hydroborating α-pinene with 9-borabicyclononane.[4]
Both of these reagents can be improved upon by using 2-ethylapopinene in place of α-pinene, 2-ethylapopinene has an ethyl group in place of the methyl in α-pinene. The additional steric bulk improves the stereoselectivity of the reduction.

Diisopinocampheylborane reacts with methanol to give diisopinocampheylmethoxyborane, which in turn reacts with an

crotyl Grignard reagent
to give B-allyldiisopinocampheylborane. This can then undergo an asymmetric allylboration to give a chiral homologated alcohol, which is a useful building block in a chiral synthesis.

References

  1. ^
    PMID 17768720
    .
  2. ISSN 0021-2148
    .
  3. ^ C. F. Lane, J. J. Daniels (1972). "(−)-Isopincampheol".
    doi:10.15227/orgsyn.052.0059
    .
  4. ^ a b c d e Brown, Herbert C.; George Zweifel (1961). "Hydroboration as a convenient procedure for the asymmetric synthesis of alcohols of high optical purity".
    doi:10.1021/ja01463a055
    .
  5. ^ Brown, Herbert C.; Veeraraghavan Ramachandran (1991). "The boron approach to asymmertric synthesis".
    S2CID 53508029
    .
  6. doi:10.1002/047084289X.rd248.pub2
    . Article Online Posting Date: September 15, 2006
  7. ^ Michael W. Rathke, Alan A. Millard. (1978). "Boranes in functionalization of olefins to amines: 3-Pinanamine". Organic Syntheses. 58: 32; Collected Volumes, vol. 6, p. 943.
  8. ^ Brown, Herbert C.; John R. Schwier; Bakthan Singaram (1978). "Simple synthesis of monoisopinocampheylborane of high optical purity".
    doi:10.1021/jo00416a042
    .
  9. ^ Ramachandran, P.Veeraraghavan; Chen, Guang-Ming; Brown, Herbert C. (1996). "Efficient general asymmetric syntheses of 3-substituted 1(3H)-isobenzofuranones in very high enantiomeric excess". Tetrahedron Letters. 37 (13): 2205–2208.
    ISSN 0040-4039
    .
  10. ^ Ramachandran, V. P.; S. Pitre; Herbert C. Brown (2002). "Selective Reductions. 59. Effective Intramolecular Asymmetric Reductions of α-,β and γ-Keto Acids with Diisopinocampheylborane and Intermolecular Asymmetric Reductions of the Corresponding Esters with B-Chlorodiisopinocampheylborane".
    PMID 12126421
    .
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