Metal-Free Synthesis of Indolines

Significance

The metal-free synthesis of indolines by phenyliodine(III) bis(trifluoroacetate) mediated amidohydroxylation of 2-allylanilines is reported. The starting anilines were synthesized by N-allylation followed by aza-Claisen rearrangement. After N-protection by benzoylation, the cyclization is effected using PIFA and proceeds presumably via amidohydroxylation, N-acylnitrenium ion formation, and intramolecular trapping of the latter by the olefin residue. The resulting aziridinium species undergoes ring opening and hydrolysis to give the final product. Although the scope of the method was not extensively studied, it was shown that substrates with substituents other than H in 4-position give higher yields than substrates with substituents in 2-position.