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Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions
Author(s) -
Chen HsinTsung,
Chen HuiLung,
Ho JiaJen
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1594
Subject(s) - chemistry , cycloaddition , steric effects , enyne , solvent effects , medicinal chemistry , aromatization , solvent , density functional theory , exothermic reaction , solvation , ene reaction , reaction mechanism , photochemistry , computational chemistry , stereochemistry , organic chemistry , catalysis
Abstract The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C 2 C 7 cyclization and more exothermic (Δ R E = −69.38 kcal/mol). For R 1 = CH 3 and t ‐Bu, the increasing barrier of the C 2 C 7 cyclization is higher than that for the C 2 C 6 cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R 1 = t ‐Bu would shift the C 2 C 7 cyclization to the [4 + 2] cycloaddition. On the other hand, for R 1 = Ph, NH 2 , O − , NO 2 , and CN substituents, the barrier of the C 2 C 6 cyclization would be more diminished than the C 2 C 7 cyclization due to strong mesomeric effect; the reaction path of C 2 C 7 cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.