Direct hydrogen abstraction stereoselective

Stereoselective radical addition on the exo-face of levoglucosenone 250 leads to the C-linked dimer 251 in a modest 26% yield. The expected competing reaction is the direct hydrogen abstraction by the initial radical species. Stereoselective hemiketal and ketone reductions afford the 1,6-anhydro derivative 252, which is deprotected and opened to give the final C-ana-log of a /3-(1 4) disaccharide 253. 

Miscellaneous Cyclohexanes. Various reactions involving hydroxylation of cyclohexane derivatives have been reported. The reaction of cyclohexanol with Fe(C10 )2 and hydrogen peroxide in acidic aqueous MeCN solutions has been shown to be very sensitive to the exact concentrations of Fe", Fe ", and perchloric acid. In MeCN, cis-cyclohexane-l,3-diol forms 72% of the product diol, i.e. hydrogen removal at C-3 occurs with some stereoselectivity cis to the hydroxy-group. In highly aqueous solutions, the dominant oxidation site is at C-4. Evidence is presented for a stepwise process involving an initial directed hydrogen abstraction, oxidation of the radical by Fe" , and stereoselective carbonium ion capture. 

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