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

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 These k values are overall rate coefficients which are related to the individual rate coefficients for the pathways leading to the cis and trans products by k = k,.,, + k,,.a,,v Rate coefficients k for cycloadditions at 333 K and various pressures and for cycloadditions at 1000 bar and several temperatures are listed in Table 1.The ratio of the two diastereomeric adducts 4 and 5 was determined off-line by HPLC of the crude reaction mixture, since it was not possible to distinguish them on-line by IR

Solvation effects drive the selectivity in Diels–Alder reaction under hyperbaric conditions

“…Generally, the more compact endo approach is favored by a HPs. 2,19,20 In some cases endo kinetic adducts are obtained under hyperbaric cycloaddition, while exo thermodynamic ones are generated by heating. 21 The activation observed in organic reactions in liquid phase is explained by the Evans-Polanyi equation, which connects a negative activation volume with the acceleration of the reaction with pressure increase.…”

Correlation between pressure and steric interactions in organic reactions

“…[42][43][44] A surprising effect was reported in the cycloaddition of 7 and 2-methyldihydrofuran (Scheme 10). 39 The reaction afforded the annulated 8 and the spiro 9 compounds.…”

Enaminones in heterocyclic synthesis: A new regioselective synthesis of 2,3,6‐trisubstituted pyridines, 6‐substituted‐3‐aroylpyridines and 1,3,5‐triaroylbenzenes

“…Enaminones are readily obtainable, versatile reagents and their chemistry has recently received considerable attention [1][2][3]. In conjunction with our interest in exploring the synthetic potential of 1-substituted-3-dimethylaminopropenones 1a-d we report here efficient syntheses of 2,3,6-trisubstituted pyridines, 6-substituted-3-aroylpyridines and of 1,3,5-triaroylbenzenes utilizing 1a-d as starting materials.…”