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, 1 H & 13 C NMR, LC–MS, and elemental analysis). Single crystal structures of both compounds crystallizes in the orthorhombic and triclinic crystal systems with Cmc2 1 and P 1 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 mm 3 and 0.250 × 0.180 × 0.100 mm 3 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.