Oxidative Rearrangement of 1‐Alkylidene‐1,2,3,4‐tetrahydro‐2‐(trichloroacetyl)isoquinolines to 1,5,6,10b‐Tetrahydro‐10b‐(trichloromethyl)‐3 H ‐oxazolo[4,3‐ a ]isoquinolin‐3‐ones

On treatment with lead tetraacetate (Pb(OAc) 4 ), the 1‐(alkylidene)‐1,2,3,4‐tetrahydro‐ N ‐(trichloroacetyl)isoquinolines 2a – 2c as well as the tribromoacetyl derivative 4 undergo an oxidative cyclization with concomitant migration of the trihalogenomethyl group to afford the 1,5,6,10b‐tetrahydro‐10b‐(trichloromethyl)‐3 H ‐oxazolo[4,3‐ a ]isoquinolin‐3‐ones 3a – 3c or the tribromomethyl derivative 6 , respectively. These tricycles are also accessible via esterification of 3,4‐dihydro‐1‐(1‐hydroxy‐1‐methylethyl)isoquinoline 8 with either trichloroacetyl chloride or tribromoacetyl bromide, respectively. A plausible mechanistic description for these reactions involves an – unprecedented – ‘intramolecular iminohaloform’ rearrangement.