Introduction
<P>Lithium amino borohydride reagents (LABs) are a new class of powerful and selective
reagents that were first introduced by Singaram et al. in 1992.
[
1a]
The reactivity of these reagents is comparable to lithium aluminium hydride. However,
they have several advantages over lithium aluminium hydride, e.g., they are air-stable,
non-pyrophoric, thermally stable and hydrolyse only slowly in protic solvents above
pH 4. Thus LABs can perform in air virtually all of the transformations for which
LAH is commonly used and offer significant advantages in safety, selectivity, and
ease of handling and simple work-up procedures. In short, LAB is an attractive alternative
to LAH or super hydride reduction.</P><P>LABs can be prepared as solids or 1-2 M THF
solutions, or they can be generated in situ for immediate use by the reaction of
n-BuLi or MeLi with amine-borane complexes to the corresponding LABs.
[
1]
LABs can be prepared from any primary or secondary amine, thus allowing precise steric
and electronic control of their reactivity by modulation of the substituents on the
nitrogen atom.</P><P>In 1995, Kagan and co-workers reported the only chiral LAB reagent.
However, the reduction of ketones using this reagent afforded the corresponding alcohols
in low ee (5-9%).
[
2]
</P>
