SYNTHESIS OF INDOLES FROM N-(TRIFLUOROACETYL)-2-ANILINO ACETALS

Article abstract of DOI:10.1021/jo00317a026

N-(trifluoroacetyl)indoles (3) are produced in high yield from appropriately ring-substituted N-(trifluoroacetyl)-2-anilino acetals (2) in boiling trifluoroacetic acid containing excess trifluoroacetic anhydride.Mild saponification provides the free indoles nearly quantitatively.The scope of the reaction is discussed.The ring closure follows solvolytic substitution of a trifluoroacetoxy group for one of the ethoxy groups in 2.The method has been extended to cyclization of N-(trifluoroacetyl)-α-anilinoacetone in hot polyphosphoric acid followed by saponification to yield 3-methylindole.