DIASTEREOSELECTIVE INTRAMOLECULAR CYCLIZATION THROUGH THE TRIPHENYLPHOSPHINE CARBON-TETRACHLORIDE SYSTEM - SYNTHESIS OF SATURATED 1,4-DIHETERO 7-MEMBERED CYCLOACETALS

Several 4-hetero-6-hydroxyalkanal dimethyl acetals cyclize to methoxy- 1,4-heteroxepanes and 7-methoxy-N-tosylperhydro-1,4-oxazepine under th e neutral and mild conditions mediated by the triphenylphosphine/carbo n tetrachloride system with high diastereoselectivity (hetero = O, S, NTs). The results are evidence of the formation of the seven-membered ion 19. Starting with 4-aza-6-hydroxy-4-methylhexanal dimethyl acetal and 6-hydroxy-4-oxahexanal ethylene acetal, under the same conditions, the corresponding 6-chloro analogues are obtained with good yields.