RESUMO
The molecular and supramolecular structures are reported of N-[2-(pyridin-2-yl)ethyl]methanesulfonamide, C8H12N2O2S, (I), N-[2-(pyridin-2-yl)ethyl]benzenesulfonamide, C13H14N2O2S, (II), and N-[2-(pyridin-2-yl)ethyl]toluenesulfonamide, C14H16N2O2S, (III). Although (II) and (III) are almost structurally identical, the N(amide)-C(ethyl)-C(ethyl)-C(pyridinyl) torsion angles for (I) and (II) are more closely comparable, with magnitudes of 175.37â (15)° for (I) and 169.04â (19)° for (II). This angle decreases dramatically with an additional methyl group in the para position of the sulfonamide substituent, resulting in a value of 62.9â (2)° for (III). In each of the three compounds there is an N-H...N hydrogen bond between the sulfonamide of one molecule and the pyridine N atom of a neighbor. Compound (I) forms hydrogen-bonded dimers, (II) uses its hydrogen bonding to connect supramolecular layers, and the hydrogen bonding of (III) connects linear chains to form layers. For arene-substituted (II) and (III), the different conformations afforded by the variable dihedral angles promote intermolecular π-π stacking in the benzene-substituted structure (II), but distorted intramolecular T-shaped π-stacking in the toluene-substituted structure (III), with a centroid-to-centroid distance of 4.9296â (10)â Å.
Assuntos
Benzeno/química , Complexos de Coordenação/química , Metano/química , Piridinas/química , Sulfonamidas/química , Cristalografia por Raios X , Ligação de Hidrogênio , Ligantes , Estrutura MolecularRESUMO
The asymmetric total synthesis of pyranicin (1) is reported. The butenolide ring was constructed via an asymmetric alkylation/ring-closing metathesis strategy. The three stereocenters in the left-hand tetrahydropyran ring were installed by sequential chiral auxiliary-mediated aldol reactions. Closure of the tetrahydropyran and fusion of the alkyl backbone were affected via a sequential ring-closing metathesis-cross-metathesis strategy.