Chiral (2,5)pyrido[7(4)]allenoacetylenic cyclophanes: synthesis and characterization.

Chiral pyridoallenophanes! The synthesis and characterization of chiral acetylenic pyridoallenophanes along with 2,4- and 2,5-pyridyl[Re(CO)(4)LBr] complexes are reported. The relative configurations of the four stereoisomers have been unambiguously assigned. Chromatographic resolution of the racemate of the C(4) stereoisomer was accomplished and mirror-image CD spectra have been obtained (see figure).Chiral macrocycles bearing four 2,5-substituted pyridine units have been prepared regioselectively. The four possible diastereoisomers (twist, chair, crown, and boat) were obtained in the reaction and separated by preparative HPLC. The isomers were fully characterized through their chirality and also their symmetry properties, taking into account the number of nonequivalent cumulenic carbon atoms in the (13)C NMR spectra. The reaction of the isolated twist cyclophane with [Re(CO)(5)Br] led to an uncommon tetracarbonyl rhenium complex [Re(CO)(4)L]. The arrangement of the ligands around the metal core was studied through the 2,4- and 2,5-bis(ethynylallenylethynylpyridyl) model compounds by analysis of their NMR, IR, and UV/Vis spectra.