Woodward modification In the Woodward modification, Woodward substituted potassium tert-butoxide for the aluminium alkoxide. The Woodward modification of the Oppenauer oxidation, also called the Oppenauer–Woodward oxidation, is used when certain alcohol groups do not oxidize under the standard Oppenauer reaction conditions. For example, Woodward used potassium tert-butoxide and benzophenone for the oxidation of quinine to quininone, as the traditional aluminium catalytic system failed to oxidize quinine due to the complex formed by coordination of the Lewis-basic nitrogen to the aluminium centre. Other modifications Several modified aluminium alkoxide catalysts have been also reported. For example, a highly active aluminium catalyst was reported by Maruoka and co-workers which was utilized in the oxidation of carveol to carvone (a member of a family of chemicals called terpenoids) in excellent yield (94%). In another modification the catalyst is trimethylaluminium and the aldehyde 3-nitrobenzaldehyde is used as the oxidant, for example, in the oxidation of isoborneol to camphor. Synthetic applications The Oppenauer oxidation is used to prepare analgesics in the pharmaceutical industry such as morphine and codeine. For instance, codeinone is prepared by the Oppenauer oxidation of codeine. The Oppenauer oxidation is also used to synthesize hormones. Progesterone is prepared by the Oppenauer oxidation of pregnenolone. A slight variation of the Oppenauer oxidation is also used to synthesize steroid derivatives. For example, an efficient catalytic version of the Oppenauer oxidation which employs a ruthenium catalyst has been developed for the oxidation of 5-unsaturated 3β-hydroxy steroids to the corresponding 4-en-3-one derivative. The Oppenauer oxidation is also used in the synthesis of lactones from 1,4 and 1,5 diols. Side reactions A common side-reaction of the Oppenauer oxidation is the base-catalyzed aldol condensation of aldehyde product, which have α-hydrogens to form either β-hydroxy aldehydes or α, ß-unsaturated aldehydes. Another side reaction is the Tischenko reaction of aldehyde products with no α-hydrogen, but this can be prevented by use of anhydrous solvents. Another general side reaction is the migration of the double bond during the oxidation of allylic alcohol substrates. See also Alcohol oxidation Pyridinium chlorochromate Jones oxidation Pfitzner–Moffatt oxidation Parikh–Doering oxidation Albright-Goldman oxidation Swern oxidation Corey–Kim oxidation Dess–Martin periodinane oxidation Ley oxidation (TPAP oxidation) TEMPO oxidation References Organic oxidation reactions Name reactions