Stereoselective synthesis of spiroethers and spiroketals via photoaddition of dihydro-4-pyrones to 1,3-dioxin-4-ones
作者:Nizar Haddad、Zehavit Abramovich、Igor Ruhman
DOI:10.1016/0040-4039(96)00602-8
日期:1996.5
intramolecular photoaddition of dihydro-4-pyrones to 1,3-dioxin-4-ones, followed by subsequent fragmentation affording a spiroether which provides, after Baeyer-Villager oxidation, the corresponding spiroketal with complete retention of configuration at the spirocenter. The configuration of this center is defined by the facial selectivity of the chiral dioxinone at the photoaddition step. Thus, this
Brominations of Cyclic Acetals from ?-Amino Acids and ?- or ?-Hydroxy Acids withN-Bromosucinimide
作者:J�rg Zimmermann、Dieter Seebach
DOI:10.1002/hlca.19870700423
日期:1987.7.8
or 2-amino-carboxylic acids are treated with N-bromosuccinimide under typical radical-chain reaction conditions (azoisobuytyronitril/CCl4/reflux). Products of bromination in the α-position of the carbonyl group of the five-membered-ring acetals are isolated or identified (2, 5, and 8; Scheme 1). The dioxanones are converted to 2H, 4H-dioxinones under these conditions (12, 14, 15, 21, and 22; Schemes
Modified Preparation of (2<i>R</i>)-2-<i>tert</i>-Butyl-6-methyl-4<i>H</i>-1,3-dioxin-4-one; a Chiral Acetylacetic Acid Derivative for the Synthesis of Enantiopure Compounds
作者:Dieter Seebach、Urs Gysel、Kurt Job、Albert K. Beck
DOI:10.1055/s-1992-34162
日期:——
An improved synthesis of the title compound in ca. 45% yield on up to a 174 mmol scale is reported. Bromination of (2R,6R)-2-tert-butyl-6-methyl-1, 3-dioxan-4-one gives a mixture of mono- and dibromides which must be purified by chromatography to remove impurities which may poision the palladium catalyst in the following dehalogenation step.