Synthesis of indole and indolenine derivatives starting from indoline‐2‐thiones

Indoline‐2‐thiones 1a‐b,d,f,h , which have at least one hydrogen at the 3‐position reacted with α‐halo ester 2a‐d , α‐halo ketones 2e‐f , and a‐bromoacetonitrile 2g to give 2‐alkylthioindole derivatives 3–11 . In a similar manner treatment of 3,3‐disubstituted indoline‐2‐thiones 1c,e with α‐halo esters 2a,c,d and α‐halo ketone 2e gave 2‐alkylthioindolenines 12–16 . Treatment of 1,3,3‐ trisubstituted indoline‐2‐thiones 1g,i with ethyl bromo‐acetate 2a resulted in recovery of starting materials. Desulfurization of indolenine 14 with triphenylphosphine gave 2‐alkylideneindoline 19 .