Synthesis and Crystal Structures of Methyl 3,4,5-Trimethoxybenzoate and 1,2-Dihydro-2,2,4-Trimethylquinoline Derivatives

Abstract

Two 1,2-dihydro-2,2,4-trimethylquinoline derivatives and two methyl 3,4,5-trimethoxybenzoate derivatives have been synthesized and their crystal structure determined by X-ray single crystal diffraction. Both methyl 3,4,5-trimethoxybenzoate derivatives: methyl 2,6-dibromo-3,4,5-trimethoxybenzoate (1) and methyl 3,4,5-trimethoxy-2-nitrobenzoate (2) crystallize in the monoclinic crystal system with a = 17.2605(5) A, b = 8.9082 (3) A, c = 8.9920 (3) A, β = 105.922 (2)°, space group Cc for 1, and a = 20.4898 (4) A, b = 9.7348 (2) A, c = 24.3911 (5) A, β = 99.457 (1)°, space group C2/c for 2. 1,2-Dihydro-8-methoxy-2,2,4-trimethylquinoline (3) crystallizes in the orthorhombic, space group Pna21, with a = 11.3745 (2) A, b = 8.0638 (1) A and c = 12.0019 (2) A, while 6-chloro-1,2-dihydro-2,2,4-trimethylquinoline (4) crystallizes in the monoclinic, space group P21/c, with a = 7.8063 (10) A, b = 17.757 (3) A, c = 7.8675 (10) A and β = 91.559 (8)°. The three-dimensional crystal packing structures of all four compounds are consolidated by a combination of van der Waals forces and weak directional hydrogen bonds, mostly though the overlap of peripheral groups with the centroids of the aromatic rings as the planar aromatic systems appeared to be displaced from each other resulting in the absence of π–π stacking intereactions usually found in the structural stacking of aromatic systems. This report deals with a comparative analysis of the crystal structures and crystal packing of two pairs of closely related molecules (1, 2) and (3, 4).