Exploitation of sugar ring flipping for a hinge-type tether assisting a [2 + 2] cycloaddition.
Methyl 3-O-p-methoxybenzyl-beta-D-xylopyranoside (2) was exploited as a novel hinge-type tether for the [2 + 2] cycloaddition of cinnamate. The major ring conformation occupied by the 2,4-dicinnamate derivative of 2 was 4C1, which extends two cinnamates along a diequatorial orientation. However, 3-O-deprotected dicinnamate 5, when in a non-polar solvent, favours the 1C4 conformation, which assists the approach of two cinnamates with the 1,3-diaxial scaffold. Photoirradiation of compound at 313 nm in CHCl3 afforded the intramolecular cycloaddition of cinnamates to give methyl beta-, delta-, and xi-truxinates in a 86 : 8 : 6 ratio after transesterification with methanol. The regio- and stereoselectivities are comparable to those reported by others for tethered cinnamates. The per-deuterated dicinnamate derivative of 5 facilitated the conformation analyses of the pyranoside rings by 1H NMR, indicating that all the products of photoirradiation had 1C4-fixed pyranosides. Excellent beta-selectivity was achieved when m-bromocinnamate was subjected to hinge-tethered [2 + 2] cycloaddition.
Yuasa
Hideya
H
Department of Life Science, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 J2-10, Midoriku, Yokohama 226-8501, Japan. hyuasa@bio.titech.ac.jp
Nakatani
Masatoshi
M
Hashimoto
Hironobu
H
D002236:Carbohydrate Conformation; D002934:Cinnamates / Q000737:chemistry; D003500:Cyclization; D006027:Glycosides / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular
D002934:Cinnamates; D006027:Glycosides; C029010:cinnamic acid