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

✍ Scribed by Tietze, Lutz F. ;Hübsch, Thomas ;Ott, Christian ;Kuchta, Gabriele ;Buback, Michael

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Volume: 1995
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199519950103

✦ Synopsis

Abstract

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, 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 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.