Transition-metal free highly selective aerobic oxidation of hindered 2-alkylindoles

A novel and easy access to highly complex 3-oxoindolin-2-ylidene derivatives from the exposure of Ugi-adducts bearing an indolyl moiety in Cs2CO3/DMF to air is reported. This is the first example of aerobic oxidation of 2-alkylindoles to 3-oxoindolin-2-ylidenes. Some advantages of this method are the use of air as oxygen source, transition metal-free reagents and simple conditions, a multicomponent and one-pot process and highly regio- and stereoselective manner to trans-3-oxoindolin-2-ylidenes.

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