C₂-symmetric bisamidines: Chiral Brønsted bases catalysing the Diels- Alder reaction of anthrones

• Deniz Akalay,
• Gerd Dürner,
• Jan W. Bats and
• Michael W. Göbel

Beilstein J. Org. Chem. 2008, 4, No. 28, doi:10.3762/bjoc.4.28

• 30 min. The best enantioselectivity, albeit low, was induced by amidine 8c (24% ee). As expected, in the presence of catalyst ent-8d product ent-3a was formed preferentially (Table 1). In a solvent screening using 10 mol% of TBDPS-protected bisamidine 8c, best results were obtained in dichloromethane

Inversion symmetry and local vs. dispersive interactions in the nucleation of hydrogen bonded cyclic n-mer and tape of imidazolecarboxamidines

• Sihui Long,
• Venkatraj Muthusamy,
• Peter G. Willis,
• Sean Parkin and
• Arthur Cammers

Beilstein J. Org. Chem. 2008, 4, No. 23, doi:10.3762/bjoc.4.23

• acceptors [2]. The intermolecular hydrogen bond between the amidine sp2-NH and the imidazole sp2-N was maintained in all crystalline phases examined. Apparently the sp2-N atom in the imidazole accepts hydrogen bonds better than the sp2-N atom in the amidine group, and the non-involvement of amidine, as the

• state motif of 2 is likely the Ci dimer and structures that successfully compete with the Ci dimer should have increased stabilities from identifiable atomic parameters. The dihedral angles, θ, between the imidazole and the amidine moieties characterize the solid-state conformation and are reported in

• Table 1. This parameter is defined in Figure 3 by the amidine N, C atoms and imidazole N, C atoms. With all else equal, molecules with θ of equal value but of opposite sign are conformational enantiomers. Even though only five structures did not crystallize as hydrogen bonded Ci dimers, comparing the

Perhalogenated pyrimidine scaffolds. Reactions of 5-chloro- 2,4,6-trifluoropyrimidine with nitrogen centred nucleophiles

• Emma L. Parks,
• Graham Sandford,
• John A. Christopher and
• David D. Miller

Beilstein J. Org. Chem. 2008, 4, No. 22, doi:10.3762/bjoc.4.22

• , many pyrimidine derivatives have been used for various medicinal applications (Figure 1) [1][2][3]. Synthesis of pyrimidine rings most commonly involves cyclocondensation reactions of amidine, guanidine or thiourea derivatives with either 1,3-diketone or 1,3-diester systems [4][5]. However, many of