SYNTHESIS, CHARACTERIZATION, THERMAL, X-RAY, AND DFT ANALYSES OF 6-TERT-BUTYL 3-ETHYL 2-[(3-METHOXY/5-BROMO)-2-HYDROXY AND (3-NITRO/3-METHOXY)BENZYLIDENEAMINO]- 4,5-DIHYDROTHIENO[2,3-C]PYRIDINE-3,6(7H)-DICARBOXYLATE

Abstract

In this work, 6-tert-butyl 3-ethyl 2-amino-4,5-dihydrothieno[2,3-c]pyridine-3,6(7H)-dicarboxylate is synthesized from starting tert-butyl 4-oxopiperidine-1-carboxylate, ethyl cyanomalonate, and sulfur, and then, coupled with same aromatic aldehyde affords the corresponding Schiff base compounds. These compounds (2a-d) are characterized using FTIR, H-1 and C-13 NMR spectroscopic methods. The crystal and molecular structure of (E)-6-tert-butyl 3-ethyl 2-((2-hydroxy-3-methoxybenzylidene)amino)-4,5-dihydrothieno[2,3-c]pyridine-3,6(7H)-dicarboxylate (2a) is characterized by the X-ray crystallographic analysis. Compound 2a crystallizes in the monoclinic space group P2(1)/c. The molecular and crystal structure is stabilized by two O-HMIDLINE HORIZONTAL ELLIPSISN and O-HMIDLINE HORIZONTAL ELLIPSISO intramolecular hydrogen bonds (OMIDLINE HORIZONTAL ELLIPSISN and OMIDLINE HORIZONTAL ELLIPSISO are 2.598(5) angstrom and 2.990(5) angstrom, respectively; O-HMIDLINE HORIZONTAL ELLIPSISN = 147 degrees and O-HMIDLINE HORIZONTAL ELLIPSISO = 134 degrees). According to DFT, compound 2d also shows the intramolecular hydrogen bonding, while there is no this type of interaction in compound 2b and 2c.