Low energy conformations of two carbohydrate-based oxepines were characterized by computational methods and 3JH,H coupling constant analysis. Oxepine reactivity in Ferrier reactions was correlated with percentage vinylogous anomeric effect (VAE).

Ferrier reactions follow a mechanistic pathway whereby Lewis acid activation of a cyclic enol ether facilitates departure of an allylic leaving group to form a glycosyl Ferrier cation. Attack on the Ferrier cation provides a new acetal linkage concurrent with the transposition of the alkene moiety. The idiosyncratic outcomes of Ferrier reactions of seven-membered ring carbohydrate-based oxepines prompted an investigation of its corresponding septanosyl Ferrier cation. Experiments that characterized the ion, including gas-phase cryogenic IR spectroscopy matched with density functional theory-calculated spectra of candidate cation structures, as well as product analysis from solution-phase Ferrier reactions, are reported here. Results from both approaches revealed an inclination of the seven-membered ring cation to contract to five-membered ring structures. Gas-phase IR spectra matched best to calculated spectra of structures in which five-membered dioxolenium formation opened the oxepine ring. In the solution phase, an attack on the ion by water led to an acyclic enal that cyclized to a C-methylene-aldehydo arabinofuranoside species. Attack by allyl trimethylsilane, on the other hand, was diastereoselective and yielded a C-allyl septanoside.

The synthesis and crystal structures of three new disubstituted [13]-macrodilactones, namely, trans-4,8-dimethyl-1,10-dioxacyclotridec-5-ene-2,9-dione, C13H20O4, I, cis-4-(4-bromophenyl)-13-methyl-1,10-dioxacyclotridec-5-ene-2,9-dione C18H21BrO4, II, and trans-11-methyl-4-phenyl-1,10-dioxacyclotridec-5-ene-2,9-dione, C18H22O4, III, are reported and their conformations are put in the context of other [13]-macrodilactone structures reported previously. Together, they show that the number, location, and relative disposition of groups attached at the termini of planar units of the [13]-macrodilactones subtly influence their aspect ratios.

A Ni-catalyzed cross-coupling is utilized as a reversed strategy for the homogeneous deprotection of benzyl ethers. The reaction is accelerated in batch using microwave heating or in flow using superheating in a plug flow reactor to achieve the desired (hetero)aromatic alcohols bearing heterocycles, alkenes, and ethers within 1 h. This work highlights an alternative debenzylation strategy in flow for cases where hydrogenation using heterogeneous catalysts is not a viable option.