Synthesis of Spiro1,4-Dihydropyridines: A Review.

The preparation of medicinally promising spiro1,4-dihydropyridines accompanied by their applications in biological and pharmaceutical activities is presented. Spiro1,4-dihydropyridines were synthesized using numerous reported methods including bronested acids such as p-TSA, AcOH, nano-ranged calix[4]arene tetracarboxylic acid, sulfamic acid, PEG-OSO3H, tetramethylguanidinium triflate; lewis acids including Zn(OTf)2, FeCl3, copper, alum, aluminosilicate nanoparticles, MnFe2O4 nanoparticles, manganese ferrite nanoparticles, BF3OEt2; under alkaline conditions such as Et3N and piperidine; ionic liquids such as [KAl(SO4)2·12H2O] and [Bmim]PF6, [MIM(CH2)4SO3H][HSO4]; and other miscellaneous procedures, for example, microwave-assisted catalyst and solvent-free conditions, using iodine, PEG-400, and NaCl.