Synthesis and crystal structures of two structurally related kryptoracemates

Abstract

Kryptoracemates are racemic compounds (pairs of enantiomers) that crystallize in Sohnke space groups (space groups that contain neither inversion centres nor mirror or glide planes nor rotoinversion axes). Thus, the two symmetry-independent molecules cannot be transformed into one another by any symmetry element present in the crystal structure. Usually, the conformation of the two enantiomers is rather similar if not identical. Sometimes, the two enantiomers are related by a pseudosymmetry element, which is often a pseudocentre of inversion, because inversion symmetry is thought to be favourable for crystal packing. We obtained crystals of two kryptoracemates of two very similar compounds differing in just one residue, namely rac-N-[(1S,2R,3S)-2-methyl-3-(5-methylfuran-2-yl)-1-phenyl-3-(pivalamido)propyl]benzamide, CHNO, (I), and rac-N-[(1S,2S,3R)-2-methyl-3-(5-methylfuran-2-yl)-1-phenyl-3-(propionamido)propyl]benzamide dichloromethane hemisolvate, CHNO·0.5CHCl, (II). The crystals of both compounds contain both enantiomers of these chiral molecules. However, since the space groups [P222 for (I) and P1 for (II)] contain neither inversion centres nor mirror or glide planes nor rotoinversion axes, there are both enantiomers in the asymmetric unit, which is a rather uncommon phenomenon. In addition, it is remarkable that (II) contains two pairs of enantiomers in the asymmetric unit. In the crystal, molecules are connected by intermolecular N-H...O hydrogen bonds to form chains or layered structures.

Bi(OTf)3-Catalyzed Diastereoselective One-Pot Synthesis of 1,3-Diamines with Three Continuous Stereogenic Centers

“…In addition, 1,3-diamines with only one or two stereogenic centers are accessible. Recently, we were able to develop a unified strategy for the modular construction of 1,3-diamines . Although, 1,3-diamines with three continuous stereocenters can be accessed in a highly stereodivergent manner, our process is based on a two-step protocol using large amounts of air- and moisture-sensitive reagents or catalysts.…”

Origin of Bismuth‐Rich Strategy in Bismuth Oxyhalide Photocatalysts

“…The results are consistent well with the available experimental data. [ 49 ] Clearly, the lattice constant shows only slight difference from F to I. In comparison, the Bi‐ X bond length gradually increases from F to I, which is attributed to the different ionic radii and electronegativity of halogen elements.…”

Chirality determination in crystals

“…56 However, kryptoramecates with an even Z 0 > 2 can also be found. For instance, Kramer and Bolte obtained crystals of two very similar compounds 62 differing in just one residue but both crystallizing in a Sohncke space group with respectively Z 0 = 2 and Z 0 = 4 (plus two CH 2 Cl 2 solvent molecules in the latter case) as illustrated in Figure 1.…”