摘要
本文探讨了4,5-二苯基噁唑及其2-取代化合物的生成机理;从而改进了由安息香制备这些噁唑化合物的实验操作,提高了产率;合成了5个2-取代的4,5-二苯基噁唑;更正了文献中的一些错误。
Since 4, 5-diphenyloxazoles are the required intermediates of a newly designed route by us for the synthesis of sesamin-group lignans, we have to investigate the synthetic methods and the formation mechanisms of the ozazoles.The reactions between the six carboxylic esters of benzoin (1a-f) and formamide demonstrated that the a1ky1 group substituted on C2 of the oxazole ring was-adopted from the R group of the carboxylic component of the benzoin ester rather than the R' of the amide. This means that the Mechanism I shown in the Scheme should be involved in the formation of oxazoles from benzoin esters. But when benzoin itself was used to react with formamide, a process similar to the Mechanism I should be operated) and if α-chloro-phenylacetophenone was used, the formation of the oxazole would be preceded by an intramolecular replacement of the α-Cl by the O of the =N- CH=O group.Based on the mechanistic study, the best procedure set to prepare 2-alkyl-4, 5-diphenyloxazoles (2b-f) was to reflux the benzoin ester (1b-f) with formamide in the presence of catalytic amount of conc. H2SO4, the yields were 50-90%; and to prepare 4, 5-diphenyloxazole (2a) from benzoin and formamide, the procedure would be the same (yield 55%), but better with an azeotropic separation of water (yield 83.3%).Because in the preparation, all the intermediates (1) and products (2) were carefully purified, the incorrect m. p. (68℃) reported in the literature for benzoin formate (1a) is now put right (73.0-74.5℃) in this paper.
出处
《北京大学学报（自然科学版）》
CAS
CSCD
北大核心
1992年第6期671-677,共7页
Acta Scientiarum Naturalium Universitatis Pekinensis
基金
国家自然科学基金
北京市科技委员会资助项目
关键词
安息香
羧酸酯
恶唑
Benzoin
Benzoin carboxylates
4, 5-Diphenyloxazoles
Synthesis
Mechanism
