A New Reduction with Hydrogen Telluride

Abstract

Development of facile synthetic methods of sodium or lithium salts of hydrogen tellu. ride and tellurols opened up a new field of tellurium chemistry, where these tellurium compounds have been used as the reducing agents. On the other hand little attention has been paid to the reactivity of hydrogen telluride itself. Since hydrogen telluride has relatively weak Te-H bonds (bond energy=64 kcal/mol), it was expected that hydrogen telluride should have a high potentiality as a reducing agent.
We examined the reactivity of hydro gen telluride generated in situ by the hydrolysis of aluminum telluride and found that hydrogen telluride had a unique reducing ability toward some specific functional groups containing nitrogen and/or oxygen atoms. For example, azo-, azoxy-, and nitrosobenzene were reduced to hydrazobenzene under mild conditions. Nitrobenzenes, phenylhydroxylamine, imines, and enamines gave corresponding amines. Aromatic aldehydes were reduced to alcohols at 0°C in quantitative yields. Reduction of aliphatic aldehydes was slow under the identical conditions. Selective reduction of C-C double bond of α, β-unsaturated carbonyl compounds was achieved at lower temperatures. As an application of this reduction system, a new convenient method for reductive alkylation of amines with carbonyl compounds by use of aluminum telluride and water has been developed. When the reaction of aliphatic aldehydes with hydrogen telluride was carried out under acidic conditions, the reduction to alcohols was suppressed resulting in the formation of dialkyl ditellurides.
Present reduction method is quite simple in the experimental procedure, so that it will be useful in organic syntheses. Especially, the applicability of D₂O as the deuterium source in the present reaction is of vital importance as demonstrated in the reduction of aldehydes.