Oxidative Rearrangement of 1-Alkylidene-1,2,3,4-tetrahydro-2-(trichloroacetyl)isoquinolines to 1,5,6,10b-Tetrahydro-10b-(trichloromethyl)-3H-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)‐3H‐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.