PURPOSE: To obtain an N-alkoxy nitrogen-containing heterocyclic compound by a simple operation in a short time in high yield, by subjecting an N-halo-O-alkylhydroxamic acid to intramolecular ring closure in an acidic solvent in the presence of a metallic ion.

CONSTITUTION: A compound shown by the formula I (Ar is aromatic ring; n is 1W4 integer; X is halogen, preferably Cl; R is alkyl) is subjected to intramolecular ring closure in an acidic solvent in the presence of a metallic ion of transition atom such as Ag+, Zn2+, Cu+, Pd2+, Fe2+, etc. under cooling W at room temp. for 10W60min with stirring, to obtain advantageously an N- alkoxy nitrogen-containing heterocyclic compound such as 1-methoxyindole, 1- methoxyoxyindole, etc. having a partial structure shown by the formula II. The compound shown by the formula I , for example, is obtained by reacting an O- alkylhydroxamic acid with a tert-butylhypohalite in the presence of a small amount of potassium carbonate in a nonaqueous solvent such as carbon tetrachloride, etc.