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Synlett 2007(6): 0995-0996  
DOI: 10.1055/s-2007-973864
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© Georg Thieme Verlag Stuttgart · New York

Lithium Amino Borohydrides (LABs)

Partha Pratim Saikia*
Natural Products Chemistry Division, Regional Research ­Laboratory, Jorhat 785006, India
e-Mail: ppsaikia@yahoo.co.in;
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Publication History

Publication Date:
26 March 2007 (online)

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Introduction

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.

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.

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]