Inter‐ and intramolecular hetero diels‐alder reactions, XXII. hetero diels‐alder reactions of enamine carbaldehydes at high pressure studied by on‐line IR detection

The hetero Diels‐Alder reaction of 1 and 2 to the 4‐aminodihydropyrans 3 and 4 in CH2Cl2 and isodurene solutions is studied between 45°C and 95°C by direct quantitative infrared spectroscopy under high pressure up to 3 kbar. The activation energies in isodurene and in CH2Cl2 are found to be 65 ± 5 kJ · mol−1, and 58 ± 9 kJ · mol−1, respectively. The activation volumes turn out to be practically identical: −25.1 ± 1.7 cm3 · mol−1 in CH2Cl2 and −25.0 ± 1.8 cm3 · mol−1 in isodurene. The promising aspects of applying high‐pressure infrared spectroscopy to the detailed kinetic study of organic reactions are indicated.