Synthesis, hydrolytic reactivity, and polymerization of 2,6‐ and 2,7‐dioxabicyclo[2.2.1]‐heptanes

Abstract 2,6‐Dioxabicyclo[2.2.1]heptane (3), the parent of a new ring system, has been synthesized by acid‐catalyzed bicyclization of 1,1‐diethoxy‐3‐hydroxymethyl‐4‐butanol. Conditions which were crucial to success included working in dilute dioctyl phthalate under high vacuum with vigorous stirring and distilling 3 as formed. 2,7‐Dioxabicyclo[2.2.1]heptane (4) was synthesized by similar acid‐catalyzed cyclization of either 5‐hydroxy‐2‐methoxytetrahydropyran or 1,1‐diethoxy‐4,5‐pentanediol. In acid‐catalyzed hydrolysis, 3 was almost one million times as reactive as dimethyl acetal, and 4 was only slightly less. General acid catalysis was observed for both during studies of hydrolysis in presence of buffers. Polymerization of 3 occurred very readily with a variety of cationic initiators. Protonic acids gave high conversion to soluble polymer which was of moderate molecular weight (ζinh = 0.35), liquid (rubber), and consisted of a 60:40 mixture of isomers (probably trans:cis) detected by NMR. Cationic polymerization of 4 also occurred readily. Again, high conversions to moderate molecular weight liquid polymer were obtained. At −78°C, the polymer contained exclusively tetrahydrofuran links; at a higher temperature, several initiators gave significant amounts of tetrahydropyran links.