ChemInform Abstract: Chiral Lactols. Part 7. O,O‐ and O,N‐Acetal Formation Using the Enantiomerically Pure exo Anellated Octahydro‐7,8,8‐trimethyl‐4,7‐methanobenzofuran‐2‐ol Protective Group.

Abstract

091ChemInform Abstract The enantiomerically pure lactol (I) exhibits anomeric and enantiomeric selectivity when treated with the racemic hydroxy compounds (II) affording the diastereomers (III) and (IV). A conformational analysis (1H, 13C NMR data) is carried out with a view to determining the absolute configuration of compounds of type (II). Compound (I) reacts with prim. amines such as (Va), (Vb) to yield anomeric mixtures whereas sec. amines (Vc), (Vd) give the O,N-acetals (VIc), (VId) exclusively. Reaction of the isomer (VIII) of (I) with the amines (V) affords the O,N-acetals (IX) and (X) (in part no yields given).

Increasing chiral recognition in acetal formation

“…Reducing the available space in that area should therefore lead to further destabilization of the BA-diastereomer. To further increase observed enantiomer selectivity 2 in acetal formation leading to BB 3 and the BA 4 diastereoisomers, 26 we planned to introduce a bulky substituent at the methyl group of the bridgehead position to interfere with the pl-substituent in the BA diasteroisomer and further to destabilize it (Fig. 2).…”