N-Methoxy-N-acylnitrenium ions (11), generated by treatment of N-chloro-N-methoxyamides with silver carbonate in trifluoroacetic acid, react with arenes to give N-aryl-N- methoxyamides in good yields. In the case of the intramolecular cyclization of N-chloro-N- methoxy-2-phenylacetamides, the mode of cyclization is highly dependent on the nature of ortho or para substituent groups. Nitrenium ions I1 can primarily attack three positions (C- ...