N. Kawai, T. Shioiri*
Aug 25, 1983
Citations
0
Influential Citations
10
Citations
Journal
Chemical & Pharmaceutical Bulletin
Abstract
Propiophenone (11) was conveniently converted to its enamines 12a-c using boron trifluoride etherate as a catalyst. Reaction of diphenyl phosphorazidate (DPPA) with the enamines 12a-c efficiently afforded the N-phosphorylated amidines 14a-c by the 1, 3-dipolar cycloaddition of DPPA to the enamine double bond, followed by the evolution of nitrogen from the intermediate triazoline 13, and 1, 2-migration of the phenyl group. 1, 3-Dipolar dlimination products 15a-c were also formed, though in very low yields. Some chemical properties of the N-phosphorylated amidine 14a, as well as the 1, 3-dipolar character of DPPA, were investigated. By the same reaction sequences (enamine formation followed by the 1, 3-dipolar cycloaddition of DPPA), some alkyl phenyl ketones 29a-c were conveniently converted to the N-phosphorylated amidines 31a, 31b, and 27 via the enamines 30a-c. However, in the case of acetophenone and its derivatives 33a-c, these reaction sequences proceeded sluggishly. Alkaline hydrolysis of the N-phosphorylated amidines 14a, 31a, 31b, and 27 with potassium hydroxide afforded 2-phenylalkanoic acids 25 and 32a-c, respectively, in excellent yields. The overall three-step process of successive treatment of alkyl phenyl ketones (alkyl〓methyl) with pyrrolidine, DPPA, and potassium hydroxide may provide a new general method for the efficient conversion of alkyl aryl ketones to 2-arylalkanoic acids.