The mass spectrometric behaviour of three 1a,3-diaryl-1,1,4, 4-tetrachloro-1a,2,3,4-tetrahydro-1H-azirino-[2,1-e][1, 6]benzothiazocines has been studied with the aid of mass-analyzed ion kinetic energy spectro--metry and exact mass measurements under electron impact ionization. All compounds show a tendency-to eliminate a neutral substituted/unsubstituted 1,1-dichlorostyrene from the eight-membered thiazocine ring to yield azirino[2,1-c][1, 4]benzothiazine ions, which can then lose a chlorine radical and a sulfur-atom to form azirino[2,1-c][1,4]benzothiazine ions and dihydroquinoline ions. All compounds could also eliminate a chlorine radical plus hydrogen chloride, stepwise or consecutively, to undergo a ring enlargement rearrangement to produce nine-membered 1, 7-benzothiazonine ions. The [M(+) - Cl] ions could undergo a four-membered ring rearrangement to yield 1,5-benzothiazepine ions by loss of 1,1-dichlorostyrene or styrene ions and HCl, and undergo alpha, alpha-cleavage to form benzothiazine ions by loss of arylchlorocyclopropane. The [M(+) - Cl - HCl] ions could further eliminate some atoms, small molecules or molecular fragments to form some abundant fragment ions. Copyright 1999 John Wiley & Sons, Ltd.