Acid-mediated intramolecular cationic cyclization using an oxygen atom as internal nucleophile: synthesis of substituted oxazolo-, oxazino- and oxazepinoisoindolinones

Efficient assembly of substituted oxazolo-, oxazino-, and oxazepinoisoindolinones (5–7, 12–15 and 19) is described in three steps according to an acidic α-oxoamidoalkylation reaction from ready available phthalic anhydride by successive imidation, sodium borohydride reduction and intramolecular cationic cyclization involving N-acyliminium species. The relative stereochemistry accompanying these reactions was also discussed.