REACTIONS OF ALDEHYDES AND KETONES

Treating a cyclic thioacetal with Raney nickel results in two hydrogen atoms replacing the sulfur ring. This provides an excellent step to reduce an aldehyde or ketone (get rid of the carbonyl). Form the thioacetal first, then desulfurize.

This reaction provides an excellent way to get rid of an aldehyde or ketone. Firstly, form the imine from the carbonyl, then treat with potassium hydroxide, water, and heat.

In the first step, a reducing agent (NaBH4 or LAH) gives a hydride. In the second step the oxide is protonated to yield a neutral product.

In the first step, the Grignard attacks the carbonyl. In the second step, the oxide is protonated by H3O+ or H2O. To form the Grignard reagent, treat an alkyl chloride or bromide with magnesium.

For this reaction, potassium cyanide may be used with either hydrogen cyanide or hydrochloric acid (safer option).

The formation of the Wittig reagent is an SN2 process, so the alkyl halide should be primary or secondary. According to the course text, convincing evidence exists that the reaction proceeds with cycloaddition to form an oxaphosphetane (the cyclic compound), while sometimes the carbon of the Wittig is shown attacking the carbonyl first to form a betaine, which then forms an oxaphosphetane.

Treatment of an aldehyde or ketone with a peroxy acid such as MCPBA yields an ester. A cyclic ester is called a lactone. The reaction is regioselective, preferring H>3˚>2˚>Ph>1˚>methyl.