PREPARATION OF QUINONE IMINE KETALS VIA INTRAMOLECULAR CONDENSATION OF AMINO-SUBSTITUTED QUINONE MONOKETALS - ANODIC-OXIDATION CHEMISTRY OF TRIFLUOROACETAMIDE DERIVATIVES OF 1,4-DIMETHOXYBENZENES AND 4-METHOXYPHENOLS

Two routes have been developed to the previously unknown quinone imine ketal moiety. One involves a sequence of anodic oxidation of the N-trifluoroacetamide of a 2-(2,5-dimethoxyphenyl)ethylamine or 3-(2,5-dimethoxyphenyl)propylamine derivative to form the respective quinone bisketal followed by basic hydrolysis of the trifluoroacetamide linkage, acidic hydrolysis of the quinone bisketal to a quinone monoketal, and intramolecular condensation to form the quinone imine ketal. This method requires an additional substituent at the 4-position (bromine or methoxy) to direct the regiochemistry of the quinone bisketal hydrolysis. The second method involves similar chemistry except that the anodic oxidation of a 4-methoxyphenol derivative directly affords the quinone monoketal. Hydrolysis of the trifluoroacetamide followed by an intramolecular condensation reaction affords the quinone imine ketal. Selected aspects of the chemistry of these compounds have been studied. Especially interesting is the reaction of a model quinone imine ketal with organolithium reagents. Either 1- or 2-substituted-5-methoxyindole is produced, depending upon the organolithium compound. © 1990, American Chemical Society. All rights reserved.