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  • Title: Diels-Alder reactions of 4-alkenylthiazoles: a new approach to thiazole functionalization.
    Author: Alajarín M, Cabrera J, Pastor A, Sánchez-Andrada P, Bautista D.
    Journal: J Org Chem; 2007 Mar 16; 72(6):2097-105. PubMed ID: 17316049.
    Abstract:
    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.
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