Diacetylenic compounds; 1, 7-diphenyl-1, 6-heptadiyne (I), N, N-bis(3-phenyl-2-propynyl) methylamine (III), bis(3-phenyl-2-propynyl) sulfide (VII) and bis(3-phenyl-2-propynyl) ether (IX) underwent intramolecular cyclization reaction by means of 14% solution of potassium tert-butoxide in tert-butyl alcohol in remarkably mild condition to aford naphthalene derivatives; 4-phenyl-2, 3-dihydro-1H-benz[f]indene (II), N-methy-4-phenyl-1, 3-dihydro-2H-benz[f]isoindole (IV), 4-phenyl-1, 3-dihydronaphtho[2, 3-c]thiophene(VIII) and 4-phenyl-1, 3-dihydronaphtho[2, 3-c]furan (X) respectively. The reaction mechanism of this cyclization was proposed.