Self-association of an indole based guanidinium-carboxylate-zwitterion: formation of stable dimers in solution and the solid state

• Carolin Rether,
• Wilhelm Sicking,
• Roland Boese and
• Carsten Schmuck

Beilstein J. Org. Chem. 2010, 6, No. 3, doi:10.3762/bjoc.6.3

• , 45141 Essen, Germany 10.3762/bjoc.6.3 Abstract The indole based zwitterion 2 forms stable dimers held together by H-bond assisted ion pairs. Dimerisation was confirmed in the solid state and studied in solution using dilution NMR experiments. Even though zwitterion 2 forms very stable dimers even in

• planarity from the rest of the molecule forcing the two monomers in dimer 2·2 to interact in a non-ideal orientation. Furthermore, the acidity of the NHs is lower than in 1 (as determined by UV-pH-titration) also leading to less efficient binding interactions. Keywords: dimerisation; molecular recognition

• stability is too large to evaluate with an estimated association constant of Kass> 1010 M−1. Even in water dimerisation still takes place (Kass = 170 M−1) [13]. The stability of the dimer 1·1 is significantly larger than the simple Coulomb-interactions of point charges, suggesting that indeed the formation

Dimerization of propargyl and homopropargyl 6-azido- 6-deoxy- glycosides upon 1,3-dipolar cycloaddition

• Nikolas Pietrzik,
• Daniel Schmollinger and
• Thomas Ziegler

Beilstein J. Org. Chem. 2008, 4, No. 30, doi:10.3762/bjoc.4.30

• catalytic amount of (EtO)3PCuI , TLC (ethyl acetate/n-hexane 1:1) revealed the formation of one faster moving product along with a complex mixture of slower moving products with mobility similar to those previously observed. Careful inspection of the products revealed that dimerisation of 4a occurred

Part 1. Reduction of S-alkyl- thionocarbonates and related compounds in the presence of trialkylboranes/air

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 45, doi:10.1186/1860-5397-3-45

• by subsequent modifications of the experimental procedure. We therefore returned our attention to the reduction of S-alkylxanthates that sometimes led to poor or irreproducible results when Method A was employed. In particular, some dimerisation of the radical generated from the xanthate was