Brønsted acid-promoted synthesis of highly functionalized tetrahydrocarbazoles from diethyl ( E )-5-diazo-4-oxohex-2-enedioate.

Brønsted acid-promoted synthesis of highly functionalized tetrahydrocarbazoles from indoles and easily accessible diethyl ( E )-5-diazo-4-oxohex-2-enedioate has been achieved. Diethyl ( E )-5-diazo-4-oxohex-2-enedioate acts as a 1,4-diacceptor and undergoes tandem Michael addition followed by nucleophilic substitution at the diazo carbon with indole in the presence of a strong Brønsted acid.