Base-Catalyzed Self-Condensation of Arylacetaldehydes: Molecular Structures of (E)-2,4-Bis(9-Anthryl)but-2-enal and (E)-2,4-Diphenylbut-2-enal

Abstract

Both 9-anthrylacetaldehyde and phenylacetaldehyde undergo stereoselective self-condensation in the presence of base to give (E)- 2,4-di(9-anthryl)but-2-enal (2a), and (E)-2,4-diphenylbut-2-enal (2b) respectively, as established by single-crystal X-ray structure determination. Crystals of (2a) are monoclinic, P2₁/n, Z 8, a 10.638(9), b 20.68(1), c 20.41(2)Ǻ, β 92.36(5)°; R was 0.061 for N_o 3476 'observed' reflections. Crystals of (2b) are monoclinic, P2₁/c, Z 4, a 5.781(2), b 23.163(8), c 9.297(5)Ǻ, β 91.54(4)°; R 0.037 for N_o 1174. In both compounds, the enal moiety assumes a virtually planar s-trans conformation, with the angles between the planes of the olefinic double bond and the adjacent aromatic π-system around 70°.