Flash vacuum pyrolysis (fvp) of some hexahydroquinazolin-4(1H)-ones

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• 作者：Walter J. Pel&#xe1 ; ez ; Zsolt Szakonyi ; Ferenc Fü ; lö ; p ; Gloria I. Yranzo
• 关键词：Flash vacuum pyrolysis ; Retro Diels– ; Alder ; Isothiocyanates ; Isocyanates
• 刊名：Tetrahedron
• 出版年：2008
• 出版时间：4 February 2008
• 年：2008
• 卷：64
• 期：6
• 页码：1049-1057
• 全文大小：370 K

文摘

Some cis/trans-2-thioquinazolin-4-ones and their 2,4-dione analogs were subjected to flash vacuum pyrolysis. The cis- and trans-thio compounds reacted at lower temperatures than the cis- and trans-dioxo analogs, showing a lower thermal stability. All of these compounds afforded similar reactions: ring opening to the corresponding iso(thio)cyanate, the loss of H^border=0> and ^border=0>NCS to form three isomeric cyclohexadienes and then aromatization to form the corresponding benzamide. The cis-dioxo compound also underwent a competitive retro Diels–Alder (RDA) reaction to form 3-phenylpyrimidine-2,4(1H,3H-dione(3-phenyluracil)) and butadiene. Kinetic measurements of the ring opening reaction supported a concerted β-elimination as the most probable mechanism.