127958-24-1Relevant articles and documents
Synthesis of 4,4-Dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles and N-Benzoyl Derivatives: Method for "Hydrolysis" of Unreactive Amides and Carbamates
Baumstark, Alfons L.,Choudhary, Anil,Vasquez, Pedro C.,Dotrong, My
, p. 291 - 294 (2007/10/02)
Addition of organolithium reagents to 4,4-dimethyl-3,5-disubstituted-4H-pyrazoles produced a series of 4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles, 2-6, in good yield.The reaction was stereoselective: addition of organolithium compounds occurred only to carbon-3 of 4,4-dimethyl-3-alkyl-5-aryl-4H-pyrazoles.The 3,4-dihydro-2H-pyrazoles were found to be of high sensitivity to oxygen.For long term storage and ease of handling, N-benzoyl derivatives were synthesized.Removal of protecting group could not be accomplished by use of many standard sets of conditions.Deprotection was accomplished in high yield by reaction of the N-benzoyl-4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles with anhydrous potassium t-butoxide in toluene in the presence of a phase transfer catalyst (18-Crown-6).Cleavage of a N-carbamate derivative was also achieved by this phase transfer approach.This methodology should be applicable to the hydrolysis of unreactive amides and carbamates in general.
