Anomeric affect

Corminboeuf, Renaud and Schiesser explored the applicability of various quantum methods to the diastereoselective radical cyclization of several bromoacetals during the Ueno-Stork reaction (Scheme 10) [22]. It is interesting to note the performance of the various methods. All of the methods employed correctly predict the anomeric affect (transition states 61, 62 were calculated to lie some 20 kJ mol above 59, 60) and the observed cis stereochemistry [23]. However, only a handful of... 

The 4,6-O-benzylidene group is also cleaved under these conditions, but the anomeric linkage between sugars is not affected. Anomeric trimethylsilyl-... 

Ziegler and coworkers prearranged a glycoside by employing a succinyl tether between C-6 of a mannosyl donor and C-3 of glucosyl acceptor [151,152]. They found that the nature of the glycosyl acceptor and the length of the tether affected the anomeric selectivity of the intramolecular mannosylation (Scheme 4.4d) [153]. 

As conformational anomeric effects represent only a fraction (—1 to —3 kcal/mol) of the global enthalpic anomeric effect or gem-dioxy stabilizing effect (—6 to —17 kcal/mol), additional factors have to be taken into account. Depending on substitution, steric factors can affect the relative stability of acetal conformers. Dubois et al.2S have demonstrated that in furanose pyranose derivatives a bulky substituent at the furanose... 

Thus, following the lowest energy pathway between minima might require C3-03 bond rotation in 8. This cursory examination indicates that, while the location of energy minima may not be affected by non-anomeric hydroxyl conformations, the relative energies of these minima may indeed depend on these conformations. 

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