Aqueous methods like the Jones oxidation are no good for this, since the aldehyde that forms is further oxidized to acid via its hydrate. The oxidizing agent treats the hydrate as an alcohol, and oxidizes it to the acid.

The key thing is to avoid water, so PCC in dichloromethane works quite well. The related reagent PDC (pyridinium dichromate) is particularly suitable for oxidation to aldehydes. Some very mild oxidizing agents are being more and more widely used for the synthesis of very sensitive aldehydes. One of these is known as TPAP (tetra-n-propylammonium perruthe nate, pronounced ‘tee-pap’). TPAP can be used catalytically, avoiding the large amounts of toxic heavy metal by-products generated by most chromium oxidations. The stoichiometric oxidant in this reaction is NMO (N-methylmorpholine-N-oxide), which is reduced to the amine, reoxidizing the ruthenium to Ru (VII).

Another important mild oxidant is a high-valent iodine compound known as the Dess Martin periodinane. It can be made from 2-iodobenzoic acid.

It will oxidize even very sensitive alcohols to carbonyl compounds—few others, for example, would give the cis-α,β-unsaturated aldehyde in the margin from a cis-allylic alcohol without isomerizing it to trans, or producing other by-products.

مواضيع ذات صلة

The Boc protecting group—gastrin and aspartame

The Cbz protecting group—oxytocin

Peptide synthesis

A survey of protecting groups

How to react the less reactive group (II): protecting groups

Chemoselectivity in the reactions of dianions

How to react the less reactive group (I): react both then ‘unreact’ one

Competing reactivity: choosing which group reacts

How to oxidize secondary alcohols to ketones

Birch reduction of arenes

Dissolving metal reductions

Getting rid of functional groups