Pyridine borane esters

Pyridin-Boran reduziert Oxime, deren Ather und Ester in Athanol/Salzsaure selektiv und in guten Ausbeuten zu Hydroxylaminen. Ester-, Aminocarbonyl-, Cyan-, Nitro- und Halogen-Gruppen werden nicht angegriffen4. Die selektiven Reduktionen gelingeneben-falls mit 9-Bora-bicyclo[3.3.1]nonan in Tetrahydrofuran5. 

The reduction of indoles by pyridine-borane in CF3COOH [K3] or BH3 THF in CF3COOH [MMl] is compatible with amide, nitrile, or ester groups. It is interesting to emphasize that LAH in ether media reduces these groups without affecting the... 

A soln. of p-bromobenzaldehyde and pyridine borane in isopropyl ether refluxed 45 min. p-bromobenzyl alcohol. Y 94%.—The reducing power of pyridine borane is considerably less than that of those hydrides heretofore used for the reduction of carbonyl compounds to the alcohol stage. Acids and acid chlorides gave lower yields and esters could not be reduced. F. e. and reductions s. R. P. Barnes, J. H. Graham, and M. D. Taylor, J. Org. Ghem. 23, 1561 (1958). 

The pyridine-borane reduction of oximines has been applied to the reduction of a-oximino-esters (51) to (52) (Scheme 32). ... 

In a novel reaction, the ester (18 Scheme 8) was heated with NaBH4 in pyridine to 115 C. The reaction was stopped at the ketal stage (19) so that overreduction to the alcohol was not possible. Overall yields of about 50% were reported but it might be noted that the other product of the reaction was the py-ridine/borane adduct C5H5N BH3, so that only a quarter of the available hydride was used in the reduction. 

Reductions. iyn-Selective reduction of 1,3-diketones and a-alkyl-p-keto esters is observed with borane-pyridine in the presence of TiCl4. On the other hand, anti-products predominate in the reduction with LiBHEt -CeCli. 

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