INDOLE SYNTHESES UTILIZING o-METHYLPHENYL ISOCYANIDES.

Article abstract of DOI:10.1246/bcsj.57.73

New indole synthesis starting with o-methylphenyl isocyanides such as o-tolyl, 2,4-xylyl, and 2,6-xylyl isocyanide is described. Treatment of o-tolyl isocyanide with LDA in diglyme at minus 78 degree C generated selectively o-(lithiomethyl)phenyl isocyanide in an almost quantitative yield, which on warming up to room temperature was cyclized to indole after aqueous workup. Similarly, 2,4-xylyl and 2,6-xylyl and 2,6-xylyl isocyanides were cyclized to 5-methylindole and 7-methylindole quantitatively. The o-(lithiomethyl)phenyl isocyanides reacted with electrophiles such as alkyl halides and alkylene oxides to give o-alkylphenyl isocyanides, which were cyclized via the lithiation at the orthobenzylic carbon to afford 3-substituted indoles.