Diacetone-galactose

These same authors also prepared the xanthates from diacetone mannose and diacetone galactose, but in no case were they able to effect the unsaturation of the xanthate according to the method of Chugaev. This was the original purpose of the investigation they had hoped for a better preparation of unsaturated compounds, as, for example ... 

Historically, the oxidation-reduction protocol was the only reliable method to prepare the y0-m<2w 6>-glycoside until the insoluble silver salt method was established. In 1972, Ekborg et al. reported the use of the 2-(9-benzoylated glucosyl bromide 51 for this purpose [83] (O Scheme 28). Glycosylation with diacetone galactose and selective deprotection of the 2 -position followed by DMSO oxidation afforded the 2-uroside which was reduced by hydrogenation over Pt. The use of the 1,2-0-orthoester for the same purpose was also reported [84]. 

One reason is that the conformation moves significantly away from the classic chair shape. This is what we see with the bis-ketal 2.10, diacetone-galactose (l,2 3,4-di-O-isopropylidene-a-D-galactopyranose). It has been drawn as an ordinary alicyclic compound in order not to prejudge its conformation. 

Diacetone glucose" "Diacetone galactose" "Dicyclohexylidene mannose"... 

Enol ether 70 and 3 equiv. of diacetone galactose 71 were treated with NIS in dichloroethane at — 40 °C. When tethering was complete, as indicated by thin layer chromatography, a further 2 equiv. of NIS and DTBMP were added to the reaction flask. After 2 days the reaction mixture was treated with acidic ion exchange resin to solely afford the P-mannoside 73 in an excellent yield of 84% (Method 6) [59]. As with Hindsgaul s methodology, competition experiments confirmed the intramolecular nature of the reaction. 

Similar brominolysis of the disarmed disaccharide donor 24 gave glycosyl bromide 25 which, after isolation as described above, was glycosylated with diacetone galactose under the agency of silver triflate [29] to give trisaccharide 27 [27]. 

The electrochemical mannosylation was extensively studied by the group of Fairbanks. a set of thiomannoside donors bearing various protecting groups at the 2-position was prepared and used in the elvco-sylation of diacetone galactose 17. 

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