3D model (JSmol)
|Molar mass||105.95 g/mol|
|Appearance||Colorless to yellow liquid|
|Density||0.890 g/cm3, liquid|
|Boiling point||66 °C (151 °F; 339 K) for THF|
|Main hazards||highly flammable|
|Safety data sheet||External MSDS|
lithium aluminium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Lithium triethylborohydride is the organoboron compound with the formula LiEt3BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful reducing agent used in organometallic and organic chemistry. It is a colorless or white solid but is typically marketed and used as a THF solution. The related reducing agent sodium triethylborohydride is commercially available as toluene solutions.
- LiH + Et3B → LiEt3BH
Its THF solutions are stable indefinitely in the absence of moisture and air.
LiBHEt3 reduces a wide range of functional groups, but so do many other hydride reagents. Instead, LiBHEt3 is reserved for difficult substrates, such as sterically hindered carbonyls, as illustrated by reduction of 2,2,4,4-tetramethyl-3-pentanone. Otherwise, it reduces acid anhydrides to alcohols and the carboxylic acid, not to the diol. Similarly lactones reduce to diols. α,β-Enones undergo 1,4-addition to give lithium enolates. Disulfides reduce to thiols (via thiolates). LiBHEt3 deprotonates carboxylic acids, but does not reduce the resulting lithium carboxylates. For similar reasons,
Epoxides undergo ring-opening upon treatment with LiBHEt3 to give the alcohol. With unsymmetrical epoxides, the reaction can proceed with high regio- and stereo- selectivity, favoring attack at the least hindered position:
Acetals and ketals are not reduced by LiBHEt3. It can be used in the reductive cleavage of mesylates and tosylates. LiBHEt3 can selectively deprotect tertiary N-acyl groups without affecting secondary amide functionality. It has also shown to reduce aromatic esters to the corresponding alcohols as shown in eq 6 and 7.
LiBHEt3 also reduces pyridine and isoquinolines to piperidines and tetrahydroisoquinolines respectively.
The reduction of β-hydroxysulfinyl imines with catecholborane and LiBHEt3 produces anti-1,3-amino alcohols shown in (8).
- Marek Zaidlewicz, Herbert C. Brown "Lithium Triethylborohydride" Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley & Sons. doi:10.1002/047084289X.rl148
- Marek Zaidlewicz, Herbert C. Brown (2001). "Lithium Triethylborohydride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rl148.CS1 maint: uses authors parameter (link)
- Brown, H.C.; Kim, S.C.; Krishnamurthy, S. "Selective reductions. 27. Reaction of alkyl halides with representative complex metal hydrides and metal hydrides. Comparison of various hydride reducing agents" J. Org. Chem. 1980, 45, 1-12. doi:10.1021/jo01293a018
- Baer, H.H.; Mekarska-Falicki, M. Can. J. Chem. 1985, 63, 3043.
- Tanaka, H.; Ogasawara, K. Tetrahedron Lett. 2002, 43, 4417.
- Blough, B.E.; Carroll, F. I. "Reduction of isoquinoline and pyridine-containing heterocycles with lithium triethylborohydride (Super-Hydride®)" Tetrahedron Lett. 1993, 34, 7239. doi:10.1016/S0040-4039(00)79297-5
- Kochi, T; Tang, T.P.; Ellman, J.A. J. Am. Chem. Soc. 2002, 124, 6518.