Cadogan–Sundberg indole synthesis

The Cadogan–Sundberg indole synthesis, or simply Cadogan indole synthesis, is a name reaction in organic chemistry that allows for the generation of indoles from o-nitrostyrenes with the use of trialkyl phosphites, such as triethyl phosphite.^{[1][2][3][4][5][6][7]}

Cadogan–Sundberg indole synthesis
Named after	John Cadogan Richard J. Sundberg
Reaction type	Ring forming reaction
Identifiers
RSC ontology ID	RXNO:0000509

Mechanism

o-nitrostyrene first reacts with triethyl phosphite, and the nitro group is converted to a nitroso group. The nitroso group then reacts with the alkene, and N-hydroxylindole is formed, which reacts again with triethyl phosphite to form the indole.^[1][2][3][4]

Application

The Cadogan–Sundberg indole synthesis has been used as an intermediate step in the total synthesis of Tjipanazole E,^[8] transforming 2-[trans-2-[5-Chloro-2-nitrophenyl)vinyl]-5-chloro-1H-indole to 5,5’-Dichloro-2,2’-biindole.