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Synlett 2009(12): 2037-2038  
DOI: 10.1055/s-0029-1217551
SPOTLIGHT
© Georg Thieme Verlag Stuttgart ˙ New York

Lithium tri-sec-Butylborohydride (l-Selectride): A Powerful and Highly Stereoselective Reducing Reagent

Hong-Juan Wang*
The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050016, P. R. of China
e-Mail: wanghjchem@gmail.com;

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Publikationsdatum:
03. Juli 2009 (online)

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Biographical Sketches

Hong-Juan Wang was born in Shijiazhuang, Hebei Province, P. R. of China. She received her B.Sc. (2007) in Chemistry from Hebei Normal University. Presently she is a postgraduate and works under the supervision of Professor Zhan-Hui Zhang at Hebei Normal University. Her research interests focus on the development of new reagents and catalysts in organic synthesis.

Introduction

Lithium tri-sec-butylborohydride (l-Selectride) is known to be an exceptionally powerful and highly stereoselective reducing agent. It has been used for the diastereoselective reduction of the ketones to give the alcohol, [¹-¹0] selective 1,4-reduction of the enones by conjugate addition of hydride to afford ketones [¹¹] [¹²] or alcohols, [¹³] conjugate reduction of exocyclic acrylonitrile derivatives, [¹4] reduction of the double bond [¹5] and iodide. [¹6] It was also found to be an efficient reagent for the desymmetrization of meso-­diesters, [¹7] dehalogenation of monohalopyridines, [¹8] rearrangement of 5-trimethylsilylthebaine, [¹9] reductive cleavage of exoxides, [²0] and deprotection of N-carbomethoxy-substituted opioids to N-noropioids. [²¹]

Lithium tri-sec-butylborohydride is commercially available, but can also be readily prepared by addition of tri-sec-butylborane to a tetrahydrofuran solution of lithium aluminium hydride at room temperature. It is obtained as colorless solution in tetrahydrofuran. [²²]

Scheme 1

Abstracts

(A) Reduction of Carbonyl Compounds to the Corresponding Alcohols: l-Selectride can be applied for the diastereoselective reduction of α′-amino enones to afford chiral β-amino alcohols. [²³] Various enantiomerically pure aziridino ketones can be stereoselectively reduced by l-Selectride to provide the corresponding alcohols with high diastereoselectivities and yields. [²4] l-Selectride is also employed for the reduction of steroidal aldehydes. [²5]

(B) Reduction of α-Diazo Esters to Hydrazones: l-Selectride reduces α-diazo esters to give anti-hydrazones as the major products in THF solution. [²6]

(C) Diastereoselective Reduction of α-Sulfinylketoximes: An ­efficient procedure for stereoselective reduction of various ­α-sulfinylketoximes to the corresponding (S)-(N-methoxyamino)sulfoxides in THF solution is achieved with l-Selectride. [²7]

(D) Reduction of N-tert-Butanesulfinyl Imines: Andersen and co-workers [²5] reduced N-tert-butanesulfinyl imines with l-­Selectride in THF to provide the corresponding secondary sulfin­amides in high yield and diastereoselectivity. Reductions of the same sulfinyl imine afforded the opposite diastereomer in high yield and selectivity by changing the reductant to NaBH4. [²8]

(E) Selective Reductions of 1-Methyl-4-phenyl-2-pyridone: Mabic and Castagnoli reported that the reaction of 1-methyl-4-phenyl-2-pyridone with l-Selectride in THF gave exclusively the 1,4-reduction product. [²9]

(F) Selective Cleavage of Carbamates: A mild method for the cleavage of a variety of carbamates has been developed using l-Selectride. The selective cleavage of methyl carbamates in the presence of more sterically demanding carbamates can be accomplished efficiently. [³0]

(G) Demethylation of Methyl Phenyl Ethers: l-Selectride has successfully been used for the deprotection of methyl phenyl ethers. [³¹] l-Selectride is also an efficient agent for the 3-O-de­methylation of opioids. [³²]

(H) Asymmetric Reductive Aldol Reaction: Ghosh et al. have demonstrated that l-Selectride can be used to mediate reductive aldol coupling of enones and optically active α-alkoxy aldehydes to provide α,α-dimethyl-β-hydroxy ketones with excellent diastereoselectivity. [³³]

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Scheme 1