Preparation of 13C4-6-methyl anthranilic ester via a Diels-Alder-type process. an experimental and theoretical study to characterize an unexpected isotope exchange.
Buta-2,3-dienoate reacts with vinyl ketenimine to give the corresponding substituted aniline through a Diels-Alder cycloaddition. Besides the expected Diels-Alder adduct 3a, the aniline 3b was also obtained in a ratio of 91:9. The observed (13)C exchange is explained on the basis of a reversible [2 + 2] cycloaddition competing with the [4 + 2] process. This is supported by B3LYP DFT computations, as a stepwise pathway lies very close in energy to the [4 + 2] concerted one. [reaction: see text]
Alonso-Gómez
J Lorenzo
JL
Departamento de Química Orgánica, Universidade de Vigo, 36310 Vigo, Spain.
Pazos
Yolanda
Y
Navarro-Vázquez
Armando
A
Lugtenburg
Johan
J
Cid
M Magdalena
MM