![]() ![]() 3,4- cis-isoquinolonic acids have been prepared in the presence of ionic liquids, trimethyl orthoformate, Yb(OTf) 3, silica sulfuric acid, sulfonic acid functionalized silica, KAl(SO 4) 2♱2H 2O, or L-proline. Recently, 3,4- trans-isoquinolonic acids have been prepared without catalyst by heating homophthalic anhydride IVa with different amines and aldehydes in the presence of Na 2SO 4 in refluxing toluene. BF 3-OEt 2, TiCl 4, InCl 3, and aspartic acid have been employed for the preparation of 3,4- trans-isoquinolonic acids. Mixtures of 3,4- cis and 3,4- trans isomers have been observed in the presence of catalytic amounts of bases (DIEA, TEA), Lewis acids (FeCl 3, AlCl 3, ZnCl 2), protic acid (HCl), or in the absence of catalyst. In addition, depending on the nature of the imine and the reaction conditions, the cycloaddition of homophthalic anhydride (HPA) IVa with imines affords the 3,4- cis product Va, 3,4- trans product Va, or a mixture of both predominantly. While the reaction conditions were less harsh when more enolizable anhydrides Iva and IVb were employed, catalysts or heating or long reactions time were necessary to isolate the CC products Va and Vb in decent yields. Generally, the reaction of succinic IIa and glutaric Iib anhydrides with imines requires forcing conditions such as reflux in benzene, toluene, or p-xylene (140 ☌) during 12–36 h. Surprisingly, despite the high interest in this transformation, the intrinsic drawbacks associated with the Castagnoli–Cushman reaction, including low reaction rates, moderate diastereoselectivity, catalyst-free, thermal-free, and limited substrate scope, have not been solved yet. Bioactive compounds and natural products. ![]()
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