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Inter‐ and intramolecular hetero Diels‐Alder reactions, 51. Intermolecular hetero Diels‐Alder reactions of enamino ketones. Effect of high pressure on the kinetics and diastereoselectivity
Author(s) -
Tietze Lutz F.,
Hübsch Thomas,
Ott Christian,
Kuchta Gabriele,
Buback Michael
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.199519950103
Subject(s) - chemistry , dichloromethane , intramolecular force , adduct , intermolecular force , kinetics , diels–alder reaction , ether , medicinal chemistry , photochemistry , organic chemistry , solvent , catalysis , molecule , physics , quantum mechanics
The hetero Diels‐Alder reaction of the enamino ketones 1b and 1c with ethyl vinyl ether (2) in dichloromethane to give the dihydropyrans 3b/4b and 3c/4c is studied at high pressure up to 5 kbar. The kinetics is measured by on‐line FT‐IR spectroscopy up to 3 kbar. The cycloadditions show a relatively high pressure‐dependent increase in diastereoselectivity in favor of the trans adducts 4b and 4c , respectively. The activation volumes at atmospheric pressure, ΔV o ≠ , are determined to be −(43.3 ± 2.1) and −(43.9 ± 2.9) cm 3 mol −1 for the reactions of 1b and 1c at 100°C in dichloromethane solution. The activation enthalpies, Δ H ≠ for the two cycloadditions at 1500 bar are (64.4 ± 0.4) kJ mol −1 and (64.0 ± 0.6) kJ mol −1. The ΔΔV o ≠values are (3.8 ± 0.3) and (4.6 ± 0.3) cm 3 mol −1 and the ΔΔ H ≠ values (1.5 ± 0.2) and (2.1 ± 0.3) kJ mol −1 , respectively.