2-Hydroxychalcones 1a, b react readily with alkyl and aryl isocyanates in the presence of potassium hydroxide to give directly the corresponding 3-alkyl- and 3-aryl-3,4-dihydro-4-phenacyl-2H-1,3-benzoxazin-2-ones 3. The 2-thione analogues 5a, b are similarly obtained by reacting 1a, b with methyl isothiocyanate. Thiones 5 are readily oxidized by yellow mercuric oxide to the corresponding oxo compounds 3. The direct formation of benzoxazinones from chalcones apparently proceeds through the intermediate formation of open chain carbamates.The latter are cleaved readily by p-toluenesulfonyl chloride under base catalysis to give the corresponding sulfonates.
2-羟基
查尔酮1a、b在
氢氧化钾存在下,容易与烷基和芳基
异氰酸酯反应,直接生成相应的3-烷基和3-芳基-3,4-二氢-4-
苯乙酰基-2H-1,3-
苯并恶唑啶-2-酮3。类似地,2-
硫代
酮类化合物5a、b是通过将1a、b与甲基异
硫氰酸酯反应获得的。
硫代酮5可以通过黄华
银氧化物容易地被氧化为相应的
酮类化合物3。
查尔酮直接生成
苯并恶唑啶酮的过程显然是通过中间体开链
氨基甲酸酯的形成进行的。后者在碱催化下容易被对甲基
苯磺酰氯裂解,生成相应的
磺酸酯。