6-Chloromethylierte 2-(tert-Butyl)-1,3-dioxan- und -1,3-dioxin-4-one aus (R)- oder (S)-4,4,4- Trichloro-3- hydroxybuttersaure
Enantiopure (2S,6R)-and (2R,6S)-2-(tert-butyl)-1,3-dioxan-3-ones (2 and 3, resp., cis-configuration) are prepared from each of the commercially available enantiomeric 4,4,4-trichloro-3-hydroxybutanoic acids and pivalaldehyde (52%, after crystallization). Bromination of 2 with NBS in CCl4 gives an unstable bromo-trichloro-dioxanone to which structure D is tentatively assigned. Passing a solution of the crude product D in Et2O through a column of acidic Al2O3, (S)-6-(bromodichloromethyl)-2-(tert-butyl)-1,3-dioxin-4-one (7) is formed (ca, 70% overall yield from 2 on a 50-mmol scale). Treatment of the crude D with Zn powder in Et2O leads to (S)-2-(tert-butyl)-6-(dichloromethyl)-1,3-dioxin-4-one (9, ca. 35% from 2 on a 20-mmol scale). Reductive dehalogenations of 2 and 7 with triphenyltin hydride can be carried out selectively to produce the (dichloromethyl)- and (chloromethyl)-dioxanones 5 and 6, resp., and the (dichloromethyl)-, (chloromethyl)-, and non-chlorinated dioxinones 9, 10, and 11, resp. (yields after distillation and chromatography 37–49%).
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