Carbenes from vilsmeier reagents by the action of bases in POCl3; the umpolung of vilsmeier reagents

Abstract

When para-substituted N-methylformanilides are treated in POCl₃ with a base, the corresponding Vilsmeier reagent formed undergoes ready deprotonation to give an aminochlorocarbene from which a range of products derive; a carba- moyl chloride, N-methylisatins, dimers [1,2-dichloro-1,2- bis(N-methyl-N-arylamino)ethenes], trimers {5,10-dimethyl- 11-(N-methyl-N-arylamino)-10H-indolo[3,2-b]quinolinium and 5,10-dimethyl-10H-indolo[3,2-b]quinolinium salts} and tetramers [1,1′-dimethyl-3,3′-bis(N-methyl-N-arylamino)-2,2-biindolyl] are isolated, depending upon the base used and the para-substituent.