作者:Frieder W. Lichtenthaler、Stephan Rönninger、Hans J. Lindner、Stefan Immel、Eckehard Cuny                                    
                                    
                                        DOI:10.1016/0008-6215(93)84097-p
                                    
                                    
                                        日期:1993.11
                                    
                                    2,6-Dihydropyran-3-ones carrying substituents at C-2 and C-6 in cis-arrangement invariably adopt half-chair conformations in which the ring oxygen and the carbon atom next to the carbonyl group are above and below, respectively, the plane formed by the other four carbon atoms, i.e., the H-2(o) or H-o(2) conformation. In the case of a trans-arrangement of 2,6-substituents, the geometry of the pyranoid ring falls into the B(o,6) half arrow right over half arrow left E(o) half arrow right over half arrow left H-2(o) or the inverse (o,6)B half arrow right over half arrow left (o)E half arrow right over half arrow left H-o(2) section of the conformational cycle, depending on the absolute configuration of the compound; for two of the dihydropyranones, 4B and 6, a unique skew-boat (SB(o,6)) conformation, fixed between the B(o,6) and E(o) geometries, was ascertained, which previously has only been observed for pyranoid enelactones.