N-(Cyanothioformyl)indoline; a new indoline ring forming reaction

Abstract

Conversion of 2-hydroxymethyl- and 2-hydroxyethylaniline with Appel salt 1 into the arylimines 3 and 4 is accompanied by formation of the chloromethyl and chloroethyl derivatives 8 and 9. Triphenylphosphine converts compound 8 into the benzothiazine 6 but the chloroethyl compound 9 gives N-(cyanothioformyl)indoline 10 (55%) rather than the analogous benzothiazepine 12. Indoline 10 is also formed from 9 with sodium hydride (45%), and from the hydroxyethyl compound 4 with mesyl chloride and triethylamine (65%) or with excess of Appel salt 1 (38%). ¹H and ¹³C NMR spectra show that the indoline exists in solution as two rotamers 10a and 10b. Indoline 10 is converted into the known cyanoformylindoline 13 by the nitrile oxide method, and is prepared independently from indoline and 4-chloro-5H-1,2,3-dithiazole-5-thione. Mechanisms are proposed for the new reactions.