Hydrogenolysis of Thioacetals

In contrast to the previous two procedures, this method of carbonyl deoxygenation requires two separate steps. It does, however, avoid treatment with strong base or acid. The first step is to convert the aldehyde or ketone into a thioacetal, as described earlier. These derivatives may be isolated and purified before continuing the reduction. The second step involves refluxing an acetone solution of the thioacetal over a reactive nickel catalyst, called Raney Nickel. All carbon-sulfur bonds undergo hydrogenolysis (the C–S bonds are broken by addition of hydrogen). In the following example, 1,2-ethanedithiol is used for preparing the thioacetal intermediate, because of the high yield this reactant usually affords. The bicyclic compound shown here has two carbonyl groups, one of which is sterically hindered (circled in orange). Consequently, a mono-thioacetal is easily prepared from the less-hindered ketone, and this is reduced without changing the remaining carbonyl function.

مواضيع ذات صلة

Organic compounds are more soluble in water as ions

Heterocyclic aromatic compounds

Hückel’s rule tells us if compounds are aromatic

Molecular orbitals and aromaticity

The π molecular orbitals of other conjugated cyclic hydrocarbons

Benzene has six π molecular orbitals

Varying the number of electrons

Heats of hydrogenation of benzene and cyclooctatetraene

? What makes benzene special

Aromaticity

Conjugation and reactivity: looking forward to Chapter 10

The amide group