Buback, M.; Abeln, J.; Hübsch, T.; Ott, Ch.; Tietze, L. F.
Effect of High Pressure on the Kinetics and Selectivity of the Intramolecular Hetero Diels-Alder Reaction of an 1-Oxa-1,3-butadiene
Liebigs Ann. 1995, 9-11.
 

The intramolecular hetero Diels-Alder reaction of the benzylidene-isoxazolone 3 giving the adducts 4 and 5 is studied in dichlormethane under high pressure up to 5 kbar. The kinetics is measured by on-line FT-IR spectroscopy up to 3 kbar. The cycloaddition shows a clear pressure-induced increase in diastereoselectivity. For the difference in activation volume ΔΔV^≠ of the reactions affording the two diastereomers, a value of -(1.6 ± 0.2) cm³ · mol^-1 is obtained. The activation volume ΔV_cis^≠ is determined to be -(19.4 ± 0.5) cm³ · mol^-1 at 343 K. The activation enthalpy and entropy, as derived from the overall rate coefficient k measured at 1000 bar, are (62.9 ± 1.7) kJ · mol^-1 (at 343 K) and -(135 ± 11) J · mol^-1 · K^-1.