Synthesis and structural characterization of two nostoclide analogues

Teixeira, R.R., Barbosa, L.C.A., Santana, J.O., Veloso, D.P., Ellena, J., Doriguetto, A.C., Drew, M.G.B. and Ismail, F.M.D. (2007) Synthesis and structural characterization of two nostoclide analogues. Journal of Molecular Structure, 837 (1-3). pp. 197-205. ISSN 0022-2860 doi: 10.1016/j.molstruc.2006.10.014

Abstract/Summary

The vinylogous aldol reaction between appropriate aldehydes and furan-based silyloxy diene synthon generated from 3-benzyl-5H-furan-2-one (3) afforded two truncated lactone analogues [compounds (4) and (5)] of nostoclides (2). The compounds were fully characterized by IR, NMR (H-1 and C-13), 2D NMR spectroscopy experiments (HMBC, HSQC and NOESY), MS spectrometry and X-ray crystallography. Compounds (4) and (5) crystallized in the space group P2(1)2(1)2(1) and P2(1)/c, respectively. Although expected correlations between hydrogen atoms in spatial close proximity were not observed for compound (5) using NMR, the stereochemistry of the exocyclic double bond of both (4) and (5) was unambiguously determined to be Z and E, respectively, using X-ray crystallography. The packing of both compounds within the crystal are stabilized by non-classical inter-molecular hydrogen bonds. DFT calculations (B3LYP/6-31+G* level) confirmed that the crystal structures possessed the lowest energies in the gas phase when compared to their geometric isomers. (c) 2006 Elsevier B.V. All rights reserved.