Clemmenson reduction

Fragmentation reactions sometimes accompany Clemmenson reduction. See Bailey, K.E. Davis, B.R. Aust. J. Chem., 1995, 48, 1827. Also see Rosnati, V. Tetrahedron Lett., 1992, 33, 4791. 

The Clemmenson reduction (Following fig.) gives a similar product but is done under acid conditions and so this is a suitable method for compounds which are unstable to basic conditions. 

Explain the fact that Wolff-Kishner reduction of A gave B but Clemmenson reduction of A gave C. 

WOLFF-KISHNER, THIOKETAL DESULFURIZATION, OR CLEMMENSON REDUCTION OF A KETONE KETHYDROGENOLYSIS KETONE PATH 1 PRIORITY 50 CHARACTER INTRODUCES GROUP... 

Weinreb exploited a synthetic strategy for the synthesis of bis indolyl maleimides to furnish maleimide 135 from indole-Grignard 134 and imide 134a [43]. DDQ mediated oxidative cyclization of 135 resulted N-benzyl imide 136. To complete the synthesis, Clemmenson reduction was performed for desymmetrizing 136, to produce the corresponding lactam 137 (Scheme 21). 

Redaction of aryl carbonyl compounds.2 This reduction has been conducted traditionally by the Clemmenson or Wolff-Kishner method or by reduction of dithioketals. Actually it can be conducted in high yield with W-7 Raney nickel in 50% aqueous ethanol (2-5 hours). Nitro, halo, and cyano groups are also reduced. Examples ... 

Since aliphatic aldehydes and ketones are not hydrogenated over palladium, this reaction provides a means of selectively removing an aromatic carbonyl group in the presence of an aliphatic aldehyde or ketone (Eqn. 18.10).32 The palladium catalyzed hydrogenolysis of aryl aldehydes and ketones is preferable to any of the chemical reduction procedures such as the Wolff-Kishner or Clemmenson reactions for the removal of an aryl carbonyl group. 

Acyl products that are formed can be reduced by reactions such as Clemmenson or Wolf-Kishner reductions. 

The carbonyl groups of aldehydes and ketones can be converted to methylene groups by Clemmenson and Wolf-Kishner reduction reactions. 

Under ordinary conditions, carbonyl groups of aldehydes and ketones will not be reduced by catalytic hydrogenation, but if Raney nickel (Ni-ff2) is used as the catalyst, then a reduction takes place giving an alcohol product. If the ketone or aldehyde is first converted to a dithiane, then Raney nickel reduction will give an alkane product (see Clemmenson and Wolff-Kishner reductions below as alternatives for this same transformation). 

This acid, the parent compound of the hydroxylated C24 5 acids, was detected as a trace component of human feces by Ali et al. in 1966 (50). It has not been detected elsewhere as a naturally occurring substance. Preparations of cholanic acid have been obtained by Clemmenson or Wolff-Kishner reduction of fully oxidized bile acids or by pyrolysis of hydroxy acids followed by hydrogenation of the resulting mixture (1). 

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