Synthesis and crystal structure of Rctt-1-(2-benzoxazolyl)-2-(4-chlorophenyl)-4-phenyl-3-(4-pyridinyl)cyclobutane

The title compound (C28H21ClN2O, M-r = 436.92) was synthesized by the cross-photodimerization of (E)-2-(2-phenylethenyl)benzoxazole and- (E)-4-[2-(4-chlorophenyl)ethenyl]pyridine in sulfuric acid solution. Its molecular structure has been unequivocally determined by X-ray crystallography. The title compound belongs to triclinic system, space group P1 with cell parameters: a 9.648(3), b = 10.458(4), c = 12.106(4) Angstrom, alpha = 89.089(7), beta= 75.644(6), 68.441(7)degrees, V = 1096.7(7) Angstrom(3), Z = 2, D-c = 1.323 g/cm(3), F(000) = 456 and mu(MoKalpha) = 0. 198 mm(-1). The final R and wR are 0.0627 and 0.1285, respectively for 1737 observed reflections with I > 2sigma(I). S = 0.921 and (Delta/sigma)(max) = 0.001. The cyclobutane ring has a puckered conformation with four different aryl groups substituted on each carbon atom. The dihedral angles of the cyclobutane ring are 20.2 and 20.6degrees. The bond distances of the cyclobutane ring are 1.541, 1.555, 1.560 and 1.563 Angstrom, respectively, which are slightly longer than that of the normal C-C single bond. The title compound is the only cross dimer and its two heteroaryl groups are situated at the trans-1,3 position of the cyclobutane ring, revealing that the cross-photodimerization proceeds in a head-to-tail pattern with high stereo-selectivity.