Selective oxoammonium salt oxidations of alcohols to aldehydes and aldehydes to carboxylic acids.

The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed.

Oxidative cleavage of benzylic and related ethers, using an oxoammonium salt.

Benzylic ethers and related ArCH(2)OR substrates are oxidatively cleaved by 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in wet CH(3)CN at room temperature to give the corresponding aromatic aldehyde and alcohol in high yield. Primary or secondary alcohol products are further oxidized by 1 to give carboxylic acids and ketones, respectively. The oxidation likely involves a formal hydride abstraction from the benzylic carbon as evidenced by slow reaction of substrates bearing electron-withdrawing substituents.

Ene-like addition of an oxoammonium cation to alkenes: highly selective route to allylic alkoxyamines.

The oxoammonium cation of 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) adds rapidly at room temperature in an ene-like fashion to trisubstituted alkenes to afford allylic alkoxyamines in high yield. [reaction: see text]