Reactivity of tetrahydrochromeno[2,3-b] indoles: chromic indicators of cyanide

摘要

The synthesis and reactivity of a tetrahydrochromeno[2,3-b]indoles are reported. Evidence for reversible ring-opening is based on H/D exchange and trapping experiments. These compounds readily undergo reaction with tetra-nbutylammonium cyanide. The cyanide reaction is 10-100× faster when the solution is irradiated with 350 nm light. Reaction with trimethylsilyl cyanide occurs only with UV irradiation demonstrating photoreactivity. The rate of tetrahydrochromeno[2,3-b]indole ring-opening is greater for (i) Me substitution at the hemiaminal carbon (compared to Ph), and (ii) substitution of fluorine at the 9-position of the indole. Under acidic conditions, the ring-opened indolium ion is observed.