The resulting THF complex is stable indefinitely in the absence of moisture and air.
Reactions
Alkyl halides are reduced to the alkanes by LiBHEt3.[3][4][2]
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.[5] LiBHEt3 can selectively deprotect tertiary N-acyl groups without affecting secondary amide functionality.[6] It has also been 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.[7] The reduction of β-hydroxysulfinyl imines with catecholborane and LiBHEt3 produces anti-1,3-amino alcohols shown in (8).[8]
Precautions
LiBHEt3 reacts exothermically, potentially violently, with water, alcohols, and acids, releasing hydrogen and the pyrophorictriethylborane.[2]
^Marek Zaidlewicz; Herbert C. Brown (2001). "Lithium Triethylborohydride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rl148. ISBN0471936235.
