Diels-Alder reactions of 4-alkenylthiazoles: a new approach to thiazole functionalization.
Somewhat unexpectedly, the computed highest occupied molecular orbital (HOMO) energies of some 4-alkenylthiazoles afforded values close to those calculated for the Danishefsky-Kitahara and Rawal dienes. In fact, 4-alkenylthiazoles behave as all-carbon dienes in Diels-Alder reactions with the participation of the formal C-C double bond of the thiazole ring and the side-chain double bond. The reactions with N-substituted maleimides, maleic anhydride, and naphthoquinone take place with high levels of stereocontrol to give the corresponding endo-cycloadducts in good to excellent yields. Depending on the dienophile, the cycloadduct further transforms under the reaction conditions through either a 1,3-hydrogen shift, dehydrogenation, or an ene reaction or Michael addition with another molecule of dienophile. These unprecedented results open new synthetic perspectives for the functionalization of the thiazole ring.
Alajarín
Mateo
M
Departamento de Química Orgánica, Facultad de Química, and Servicio de Instrumentación Científica, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain. alajarin@um.es
Cabrera
José
J
Pastor
Aurelia
A
Sánchez-Andrada
Pilar
P
Bautista
Delia
D
D000466:Alkadienes; D008299:Maleic Anhydrides / Q000737:chemistry; D008301:Maleimides / Q000737:chemistry; D008958:Models, Molecular; D009285:Naphthoquinones / Q000737:chemistry; D013844:Thiazoles / Q000737:chemistry*
D000466:Alkadienes; D008299:Maleic Anhydrides; D008301:Maleimides; D009285:Naphthoquinones; D013844:Thiazoles