Spirodiepoxides: Heterocycle Synthesis and Mechanistic Insight

In concert but out of sync: Reactions of spirodiepoxides (SDEs) with an amide, amidine, and thioamide and the first crystal structure of an SDE are reported (see scheme for reaction with amide; DMDO=2,2‐dimethyldioxirane). Nucleophilic SDE opening is rationalized in terms of a reactivity continuum involving the concerted, asynchronous opening of both epoxides, which is facilitated by coordination to the oxygen atom destined to become the hydroxy group.