EFFECT OF HIGH-PRESSURE ON THE KINETICS AND SELECTIVITY OF THE INTRAMOLECULAR HETERO-DIELS-ALDER REACTION OF AN 1-OXA-1,3-BUTADIENE

The intramolecular hetero Diels-Alder reaction of the benzylidene-isox azolone 3 giving the adducts 4 and 5 is studied in dichlormethane unde r high pressure up to 5 kbar. The kinetics is measured by on-line FT-I R spectroscopy up to 3 kbar. The cycloaddition shows a clear pressure- induced increase in diastereoselectivity. For the difference in activa tion volume Delta Delta V-not equal of the reactions affording the two diastereomers, a value of -(1.6 +/- 0.2) cm(3) . mol(-1) is obtained. The activation volume Delta V-cis(not equal) is determined to be -(19 .4 +/- 0.5) cm(3) . mol(-1) at 343 K. The activation enthalpy and entr opy, as derived from the overall rate coefficient k measured at 1000 b ar, are (62.9 +/- 1.7) kJ . mol(-1) (at 343 K) and -(135 +/- 11) J . m ol(-1). K-1.