Catalyst-Free Solid Phase Microwave-Assisted Synthesis of 1,4-Dihydropyridine Derivatives and Their Single Crystal Structure Determination

Catalyst-free solid phase Hantzsch synthesis of symmetric 4-(3-bromo-4-hydroxy-5-methoxyphenyl)-2,6-dimethyl-3,5-dicarbethoxy-1,4-dihydropyridine (4 a) and 4-(3-bromo-4-hydroxy-5-methoxyphenyl)-2,6-dimethyl-3,5-dicarbmethoxy-(4-nitrophenyl)-1,4-dihydropyridine (4 b) was carried out at 400 W under the microwave irradiation. The molecular crystal of both compounds were developed in a suitable solvents and characterized by X-ray crystallographic method along with other spectroscopic techniques (viz., FT-IR, 1H & 13C NMR, LC–MS, and elemental analysis). Single crystal structures of both compounds crystallizes in the orthorhombic and triclinic crystal systems with Cmc21 and P1 space groups consisting a=13.5755(13) Å, b=9.6755(9) Å, c=17.7625(17) Å, α=72.837(2)°, β=88.273(2)°, γ=75.221(2)° and a=8.9877(14) Å, b=11.1543(17) Å, c=12.2365(19) Å, α=90.00°, β=90.00°, γ=90.00° cell parameters, with 0.150 × 0.150 × 0.100 mm3 and 0.250 × 0.180 × 0.100 mm3 crystal size respectively. The 1,4-DHP ring of both compounds have adopted a flattened boat-type conformation and shows one and four intermolecular hydrogen bonds, respectively.