The combination of the Biginelli reaction with click chemistry has been used for the one-pot synthesis of 1,2,3-triazole linked dihydropyrimidinones from azides, aromatic aldehydes containing a propargyl ether group, urea, and 1,3-dicarbonyl compounds using Cu(OAc)(2)/sodium ascorbate as catalyst in acetic acid under mild reaction conditions.
KAl(SO 4 ) 2 .12H 2 O is found to catalyze efficiently the stereoselective cyclocondensation of homophthlic anhydride with imines under mild conditions to afford the corresponding cis-isoquinolonic acids in good yields.Isoquinolonic acids have been reported as starting materials for the total synthesis of natural compounds such as nitidine chloride, 1 4-epicorynoline, corynoline, 6-oxocorynoline 2 and decumbenine B. 3 In addition, isoquinolonic acids show some pharmacological and biological activities 4 including anti-inflammatory and psychotropic.There exist numerous methods for the synthesis of isoquinolonic acids and their derivatives. 5 By various catalysts such as Lewis acids (ZnCl 2 , FeCl 3 , AlCl 3 ), protic acids (CH 3 COOH, HCl), or bases (TEA, DIEA) etc., a mixture of cis-and trans-products or complicated mixtures were formed. Recently, BF 3 -Et 2 O 6 and trimethyl orthoformate 7 have been employed for the preparation of trans-isoquinolonic acids, and ionic liquids 8 have been employed for the synthesis of cis-isomers.In view of our general interest in the chemistry of imines, 9 we wish to report the stereoselective synthesis of cis-isoquinolonic acids. In this direction, the use of a KAl(SO 4 ) 2 .12H 2 O (alum), which is relatively nontoxic and inexpensive, is the center of our study. 10 In the course of our research on application of KAl(SO 4 ) 2 .12H 2 O in organic reactions, we have found that alum was an effective promoter in the preparation of cis-isoquinolonic acids.When a mixture of homophthalic anhydride (1) and imine 11 (2a) in acetonitrile was stirred at rt in the presence of a catalytic amount (0.5 equiv. mol) of alum, the reaction was completed within 8 h. Work-up of the reaction mixture showed that isoquinolonic acid (3a) was prepared in 91% yield (Scheme 1).
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