Moore-Type Cyclization Leading to Arene Chromium Tricarbonyl 1,4-Diradical Intermediates and the Isolation of Indolines

摘要

Compounds containing the 5-hydroxyindole unit are among the most active compounds in the central nervous system. A convergent approach to this unit is possible on paper from the intramolecular benzannulation reaction of carbene complex 1 where both rings of the indoline unit are generated in a single step. It has long been known that the reactions of aryl amino carbene complexes with alkynes proceed to give five-membered-ring annulated products. In contrast, it has recently been found that alkenyl amino complexes react with alkynes to produce six-membered-ring annulated products that contain a phenol function. As a result of these observations, the intramolecular benzannulation of vinyl amino carbene complexes of the type 1 (Scheme 1) promised to provide a new and straightforward approach to the synthesis of 5-hydroxy'indoles. However, we have found that this will not be possible since, for example, thermolysis of complex 1 (R~2 = H, R~1 = Ph) produces the 1-azabicyclooctane 3 rather than the 5-hydroxyindoline 2.