67174-28-1Relevant articles and documents
New Methods and Reagents in Organic Synthesis. 34. Diphenyl Phosphorazidate (DPPA) as a 1,3-Dipole. A Simple, Efficient Conversion of Alkyl Phenyl Ketones to 2-Phenylalkanoic Acids
Kawai, Nobutaka,Shioiri, Takayuki
, p. 2564 - 2573 (2007/10/02)
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 elimination 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 (alkylmethyl) with pyrrolidine, DPPA, and potassium hydroxide may provide a new general method for the efficient conversion of alkyl aryl ketones to 2-arylalkanoic acids.Keywords - enamine; diphenyl phosphorazidate; boron trifluoride etherate; 1,3-dipolar cycloaddition; 1,2-migration; N-phosphorylated amidine; alkaline hydrolysis; alkyl aryl ketone; 2-arylalkanoic acid
