The unambiguous synthesis and NMR assignment of 4-alkoxy and 3-alkylquinazolines |
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Authors: | Marcel Špulák Zdeněk Novák Karel Palát Jiří Kuneš Jana Pourová Milan Pour |
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Affiliation: | 1. Department of Inorganic and Organic Chemistry, Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, CZ-500 03 Hradec Králové, Czech Republic;2. Department of Pharmacology and Toxicology, Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Heyrovského 1203, CZ-500 03 Hradec Králové, Czech Republic |
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Abstract: | Contrary to a number of reports, alkylations of the privileged 3,4-dihydroquinazoline scaffold provide N3-alkylated products, and not 4-alkoxyquinazolines. To correctly assign the structure, 13C NMR shifts of the –Z–CHn– (Z=O, N) fragment are necessary; resonances in the 45–55 ppm range are indicative of N3-alkylation. Treatment of 3,4-dihydroquinazoline-4-one with p-TsCl afforded the N3-tosylated compound, whose reaction with an amine yielded the corresponding N3-alkyl derivative. A mechanism corroborated by 15N-labeling involving pyrimidine ring opening and recyclisation is proposed. Finally, the unambiguous preparation of 4-alkoxyquinazolines is described via treatment of 3,4-dihydroquinazoline-4-ones with PCl5 followed by an alkoxide. |
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