[112]. Wide variety of diols was applicable for this catalytic system, selectively
giving lactones in good to high yields.
The same group also reported the synthesis of γ-butyrolactone in excellent yield
via the dehydrogenative lactonization of 1,4-butanediol catalyzed by Ir complex 26
(Scheme 52) [113] under neat conditions at 140
C. The reverse hydrogenation could
be accomplished using the same catalyst, and the reversible catalytic interconversion
of 1,4-butanediol to γ-butyrolactone was therefore regarded as a promising prototype
of a hydrogen storage system.
Fujita and Yamaguchi et al. reported the dehydrogenative oxidation of primary
benzylic alcohols to benzoic acid derivatives under aqueous reflux conditions
catalyzed by a water-soluble Ir complex 53 (Scheme 53) [99], suggesting that this
transformation involves the dehydrogenation of the primary alcohol to an aldehyde,
the hydration of this aldehyde to afford a gem-diol, and the dehydrogenation of the
gem-diol to afford a carboxylic acid.
A versatile catalytic system for the dehydrogenation of primary alcohols to
carboxylic acids under basic aqueous conditions in the presence of an Ir catalyst
66 with a bipyridonate ligand bearing N,N-dimethylamino substituents was reported
by Fujita et al. [114] (Scheme 54). The carboxylic acids were obtained after acidic
work-up, and the developed methodology was successfully applied to the quantitative synthesis of acetic acid starting from an ethanol–water solution.
Williams et al. have recently developed an efficient catalytic system for the
dehydrogenative oxidation of primary alcohols to carboxylic acids [115]. Various
types of alcohols (R ¼ alkyl, aryl, and heteroaryl) were converted to the
corresponding carboxylic acids in the presence of Ir complex 67 as a catalyst after
acidic work-up (Scheme 55).
Scheme 52 Dehydrogenative lactonization of 1,4-butanediol to γ-butyrolactone
Scheme 53 Conversion of primary benzyl alcohols to benzoic acids in water catalyzed by 53
34
T. Shimbayashi and K. Fujita
giving lactones in good to high yields.
The same group also reported the synthesis of γ-butyrolactone in excellent yield
via the dehydrogenative lactonization of 1,4-butanediol catalyzed by Ir complex 26
(Scheme 52) [113] under neat conditions at 140
C. The reverse hydrogenation could
be accomplished using the same catalyst, and the reversible catalytic interconversion
of 1,4-butanediol to γ-butyrolactone was therefore regarded as a promising prototype
of a hydrogen storage system.
Fujita and Yamaguchi et al. reported the dehydrogenative oxidation of primary
benzylic alcohols to benzoic acid derivatives under aqueous reflux conditions
catalyzed by a water-soluble Ir complex 53 (Scheme 53) [99], suggesting that this
transformation involves the dehydrogenation of the primary alcohol to an aldehyde,
the hydration of this aldehyde to afford a gem-diol, and the dehydrogenation of the
gem-diol to afford a carboxylic acid.
A versatile catalytic system for the dehydrogenation of primary alcohols to
carboxylic acids under basic aqueous conditions in the presence of an Ir catalyst
66 with a bipyridonate ligand bearing N,N-dimethylamino substituents was reported
by Fujita et al. [114] (Scheme 54). The carboxylic acids were obtained after acidic
work-up, and the developed methodology was successfully applied to the quantitative synthesis of acetic acid starting from an ethanol–water solution.
Williams et al. have recently developed an efficient catalytic system for the
dehydrogenative oxidation of primary alcohols to carboxylic acids [115]. Various
types of alcohols (R ¼ alkyl, aryl, and heteroaryl) were converted to the
corresponding carboxylic acids in the presence of Ir complex 67 as a catalyst after
acidic work-up (Scheme 55).
Scheme 52 Dehydrogenative lactonization of 1,4-butanediol to γ-butyrolactone
Scheme 53 Conversion of primary benzyl alcohols to benzoic acids in water catalyzed by 53
34
T. Shimbayashi and K. Fujita