L-selectride
Names
IUPAC name
lithium tri-sec-butyl(hydrido)borate(1-)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.049.166
EC Number
  • 254-101-1
UNII
  • InChI=1S/C12H28B.Li/c1-7-10(4)13(11(5)8-2)12(6)9-3;/h10-13H,7-9H2,1-6H3;/q-1;+1 ☒N
    Key: ACJKNTZKEFMEAK-UHFFFAOYSA-N ☒N
  • InChI=1/C12H28B.Li/c1-7-10(4)13(11(5)8-2)12(6)9-3;/h10-13H,7-9H2,1-6H3;/q-1;+1
    Key: ACJKNTZKEFMEAK-UHFFFAOYAI
  • [Li+].CCC(C)[BH-](C(C)CC)C(C)CC
Properties
C12H28BLi
Molar mass 190.10 g/mol
Appearance Colorless liquid
Density 0.870 g/ml
Reacts with water
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Water reactive, flammable, burns skin and eyes
Flash point -17 °F
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

L-selectride is a organoboron compound with the chemical formula Li[(CH3CH2CH(CH3))3BH]. A colorless salt, it is usually dispensed as a solution in THF. As a particularly basic and bulky borohydride, it is used for stereoselective reduction of ketones..[1]

Use in synthesis

Like other borohydrides, reductions are effected in two steps: delivery of the hydride equivalent to give the lithium alkoxide followed by hydrolytic workup:

R2CO + Li[(CH3CH2CH(CH3))3BH] → R2CHOLi + (CH3CH2CH(CH3))3B
R2CHOLi + H2O → R2CHOH + LiOH

The selectivity of this reagent is illustrated by its reduction of all three methylcyclohexanones to the less stable methylcyclohexanols in >98% yield.[1]

Under certain conditions, L-selectride can selectively reduce enones by conjugate addition of hydride, owing to the greater steric hindrance the bulky hydride reagent experiences at the carbonyl carbon relative to the (also-electrophilic) β-position.[2] L-Selectride can also stereoselectively reduce carbonyl groups in a 1,2-fashion, again due to the steric nature of the hydride reagent.[3]

It reduces ketones to alcohols.[4] Aprepitant is another synthesis example where L-selectride was used.

N-selectride and K-selectride are related compounds, but instead of lithium as cation they have sodium and potassium cations respectively. These reagents can sometimes be used as alternatives to, for instance, sodium amalgam reductions in inorganic chemistry.[5]

References

  1. 1 2 Zaidlewicz, Marek; Brown, Herbert C. (2001). "Lithium Trisiamylborohydride". Encyclopedia of Reagents for Organic Synthesis (EROS). doi:10.1002/047084289X.rl151. ISBN 0-471-93623-5.
  2. ↑ Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. p. 685. ISBN 978-0-19-850346-0.
  3. ↑ Scott A. Miller and A. Richard Chamberlin (1989). "Highly selective formation of cis-substituted hydroxylactams via auxiliary-controlled reduction of imides". J. Org. Chem. 54 (11): 2502–2504. doi:10.1021/jo00272a004.
  4. ↑ S. D. Knight, L. E. Overman and G. Pairaudeau (1993). "Synthesis applications of cationic aza-Cope rearrangements. 26. Enantioselective total synthesis of (−)-strychnine". J. Am. Chem. Soc. 115 (20): 9293–9294. doi:10.1021/ja00073a057.
  5. ↑ Gladysz, J. A.; Williams, G. M.; Tam, Wilson; Johnson, Dennis Lee; Parker, David W.; Selover, J. C. (1979). "Synthesis of metal carbonyl monoanions by trialkylborohydride cleavage of metal carbonyl dimers: A convenient one-flask preparation of metal alkyls, metal acyls, and mixed-metal compounds". Inorganic Chemistry. 18 (3): 553–558. doi:10.1021/ic50193a006.
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