Zur Dimerisierung von Indolizinen an Palladium‐Kohle

Abstract

Dimerisation of Indolizines by Palladium Coal Oxidative dimerisation of some indolizines by Pd/C in p‐xylene was undertaken in order to evaluate reaction conditions for cyclophane syntheses. Surprisingly, alkylation by the solvent occurred at the 3‐position of the indolizines 2 and 5 as a side reaction. In toluene, yields of alkylation products 4b and 8 exceeded those of dimerisation products 3 and 6. The alkylation by the solvent was fully suppressed by using chlorobenzene or chlorotoluene. Alkylation products of indolizines with p‐xylene or toluene and previously unknown dimeric indolizines are described.

Experimental and Computational Exploration of Indolizinyl Carbene Generation. A Route to Biindolizines

“…Surprisingly, compound 8 suffered a spontaneous reaction that led to a single product in 60% yield (Scheme ). The spectral data were consistent with the biindolizine structure 7 , whose 13 C chemical shifts were nearly identical with those already reported . According to M06/6-31+G** computations, structure 7 presents two possible conformations of C 2 symmetry, s-cis and s-trans, with N−C−C−N dihedral angles of 64 and 134°, respectively, the trans form being slightly higher in energy (0.7 kcal/mol) than the cis.…”

Novel Redox-Active Cyclophanes Based on 3,3‘-Biindolizines: Synthesis and Chirality

“…The angle between the two indolizines is 62° in 3d/1 according to X-ray analysis and thus corresponds to the calculated angle of simple, unbridged 3,3‘-biindolizines. Cyclic voltammetry revealed 3d/1 to be a stable and reversible redox system similar to unbridged biindolizines. ,, The torsion angle between the two indolizines in 3d/2 is 108° in the crystal. Formation of the E -isomer is impossible because of the location of the bridge in 3d/2.…”

“…Upon oxidation, indolizines easily undergo dimerization by C−C-bond formation at their 3-positions . On oxidation of compound 1 (spacer = 1,4-C 6 H 4 ; R 1 = CH 3 ), we observed mixtures of dehydro-dimers and -trimers and higher dehydro-oligomers . The tendency toward formation of higher oligomers is probably due to the rigid spacer group.…”

Diastereoisomerism and electrochemical behaviour— an investigation of redox-active cyclophanes

“…1 We used as electroactive unit 3,3Ј-biindolizine known as a reversible two step redox system. 2- 5 The synthesized macrocycles contain three independent elements of chirality as a result of the ansa-chirality of cyclophanes and the atropisomerism of the 3,3Ј-biindolizines. It was possible to isolate pure diastereomers of the macrocycles.…”