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1.9.5.2 Aromatization

DDQ is an effective reagent for the dehydrogenation of hydroaromatic compounds to give aromatic compounds. The procedure can be applied for the synthesis heterocyclic compounds such as pyrroles, pyrazoles, indoles, furans and thiophenes. Many substituents do not interfere in the reaction. For example, using DDQ in boiling benzene tetralin and acenaphthene can be converted into naphthalene and acenaphthylene, respectively (Scheme 5).

Scheme 5

In the case of hydroaromatic compound with blocking group rearrangement has been observed. For example, in 1,1-dimethyl-1,2,3.4-tetrahydronaphthalene, the aromatization takes place with 1,2-rearrangement of the methyl group (Scheme 6).

Mechanism

Scheme 6

This process has been extensively used in steroid chemistry for aromatization. For example, DDQ has been used for aromatization in the synthesis of equilin (Scheme 7).

Scheme 7