The synthesis and structural characterisation of a series of hydrophobic piperidones and bispidones

A series of dipyridin-2-yl-substituted piperidones with alkyl chains of variable length [CH3(CH2)n-], n = 0, 5, 11, 17, have been synthesised. The piperidones are all crystalline materials and exist in the solid state as the enol tautomers, which are stabilised by hydrogen bonding. The hydrogen bonding accounts for the crystallinity of these materials, despite the presence of long alkyl chains, and extensive hydrophobic regions are observed in the extended structures of some of these molecules. A series of twelve bispidones have been synthesised from their piperidone precursors by a condensation reaction with N,N-disubstituted diamines, H2N(CH 2)2-NR2 (R = Me, Et, iPr). Solid-state structures have been obtained for three of these bispidones, all of which display a double-chair conformation. The structures show a high degree of preorganisation for metal coordination, and hence are suitable candidates for coordination complexes, where these bispidones are capable of acting as pentadenate ligands. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.