Best Synthetic Methods Oxidation and Reduction

Direct reduction of an aldehyde or ketone to the corresponding ether could potentially telescope two reactions, reduction and protection, into one step. S. Chandrasekhar of the Indian Institute of Chemical Technology, Hyderabad, reports (Tetrahedron Lett. 2004,45,5497) that in the present of polymethylhydrosiloxane (PMHS) and catalytic B(C,F,) TMS ethers of alcohols will convert aldehydes to the corresponding dialkyl ethers. The reaction works well for both saturated and benzylic alcohols. This may prove to be a useful alternative to Williamson synthesis for the preparation of complex ethers. 

Hydrogen peroxide is an inexpensive oxidant, but it requires a catalyst to effect oxidation of an alcohol to the ketone. Removal of the catalyst then becomes an issue. Ronny Neumann of the Weizmann Institute of Science reports (J. Am. Chem. Soc. 2004,126, 884) the development of a hybrid organic-tungsten polyoxometalate complex that is not soluble in organic solvents, but that nonetheless catalyzes the hydrogen peroxide oxidation of alcohols to ketones. The solid catalyst is removed by filtration after the completion of the reaction. The catalyst retained its activity after five recyles. 

In the latest development of his elegant work with hydrazone derivatives, Andrew Myers of Harvard reports (J. Am. Chem. Soc. 2004,126, 5436) that Sc(OTf), catalyzes the addition of l,2-bis(f-butyldimethylsi)yl)hydrazine, to aldehydes and ketones to form the r-butyidimethylsilylhydrazones. Addition of tBuOH/tBuOK in DMSO to the crude hydrazone effects low temperature Wolff-Kishner reduction. Alternatively, halogenation of ketone hydrazones can lead to vinyl halides such as 11, or the 1,1 -dihalo derivatives, depending on conditions. Halogenation of aldehyde hydrazones provides the 1,1-dihalo derivatives such as 13. 

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Best Synthetic Methods Enantioselective Oxidation and Reduction... 

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