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Inter‐ and Intramolecular Hetero Diels‐Alder Reactions, 49 [1] Kinetics and Selectivity of the Intramolecular Hetero Diels‐Alder Reaction of 1‐Oxa‐1,3‐butadienes using a Benzylidenebarbituric Acid Derivative Effect of Pressure, Temperature, and Solvent
Author(s) -
Buback Michael,
Gerke Kerstin,
Ott Christian,
Tietze Lutz F.
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.1491271124
Subject(s) - chemistry , intramolecular force , diels–alder reaction , selectivity , intramolecular reaction , derivative (finance) , medicinal chemistry , alder , kinetics , organic chemistry , stereochemistry , catalysis , ecology , physics , quantum mechanics , financial economics , economics , biology
The intramolecular hetero Diels‐Alder reaction of the benzy‐lidenebarbituric acid derivative 1 to give the ortho and meta products 2 and 3 is studied under high pressure up to 6 kbar in various solvents. The kinetics is measured by on‐line FT‐IR spectroscopy up to 3 kbar. The cycloaddition shows a pressure‐dependent increase in regioselectivity in favour of the ortho adduct 2. The activation volumes, ΔV, are determined to be ‐(33.1· 1.2) and ‐(34.2· 1.5) cm 3 · mol −1 for the reactions in dichloromethane and tetrahydrofuran at 100°C, respectively. For the cycloaddition in toluene and acetonitrile the activation volumes are found to be ‐(13.4· 1.5) and ‐(17.0· 4.1) cm 3 · mol −1 , respectively. Contrary to the large solvent effect on the activation volume, only a minor effect on the activation volume differences, ΔΔV, is observed. Measurement of the molar volumes of 1 and the cycloadducts 2 and 3 show a strong solvent dependency.