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Inter‐ and intramolecular hetero Diels‐Alder reactions, 52. Effect of high pressure on the kinetics and selectivity of the intramolecular hetero Diels‐Alder reaction of an 1‐oxa‐1,3‐butadiene
Author(s) -
Buback Michael,
Abeln Johannes,
Hübsch Thomas,
Ott Christian,
Tietze Lutz F.
Publication year - 1994
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199519950104
Subject(s) - chemistry , intramolecular force , diels–alder reaction , kinetics , enthalpy , cycloaddition , adduct , diastereomer , medicinal chemistry , selectivity , photochemistry , stereochemistry , organic chemistry , catalysis , thermodynamics , quantum mechanics , physics
Abstract 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) cm 3 · mol −1 is obtained. The activation volume ΔV cis ≠is determined to be ‐(19.4 ± 0.5) cm 3 · 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 .