Further investigations probed the effect of variation within the N(4)-substituent, as well as the incorporation of C(5)-or C(6)geminal substituents with a C(4)-benzyl substituent as standard. Variation of the N(4)-substituent showed that N-Me, N-allyl, Nphenyl and N-PMB were all tolerated well, with in each case <5% of the corresponding diacylated acyclic products observed, giving the desired lactol esters 49, 51, 53 and 55 in 67% to 88% yield and excellent enantioselectivity (up to 99:1 er). The incorporation of geminal substituents at C(5)-or C(6)-was predicted to perturb the rate of equilibration between ring-opened and ring-closed forms, with the Thorpe-Ingold effect expected to give a significant bias towards the cyclic lactol form at equilibrium. Furthermore, geminal substitution at C(5)-or C(6)-was expected to lead to increased substitution in the vicinity of the alcohol in the acyclic ring-opened form thus disfavouring acylation.