Critical control by scaffold flexibility achieved in diastereodifferentiating photocyclodimerization of 2-anthracenecarboxylate

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By progressively increasing the flexibility of chiral vicinal diol scaffold (from rigid cyclic tetrasaccharide to flexible 2,3-butanediol via glucose and trans-1,2-cyclohexandiol) in the diastereodifferentiating photocyclodimerization to head-to-head (HH) dimers of 2-anthracenecarboxylate on the scaffold, the anti/syn preference was dramatically inverted from 42:1 to 1:12, while the enantiomeric excess of the chiral anti-HH dimer was consistently kept high at >99% due to the excited-state dynamics that strongly disfavors the si–si enantiotopic face attack against the antipodal re–re face attack, exclusively affording the (P)-enantiomer.