The treatment of 3‐bromo‐2H‐chromene (7), dissolved in furan, 2‐methylfuran, or 2,5‐dimethylfuran, with potassium tert‐butoxide, leads to formation of the epoxybenzo[c]chromene derivatives 8−11 in yields of 28−59%. Likewise, in styrene solution, exo‐2‐phenylcyclobuta[b]chromene 12 is produced (41% yield). With tetrahydrofuran as the solvent, 2‐tert‐butoxy‐2H‐chromene (13) is observed as the only product (79% yield). From these results, it is concluded that 7 is converted by β‐elimination into the title compound 5. This reactive intermediate is then intercepted by the furans and styrene in cycloaddition reactions to give compounds 8−12, whereas reaction with KOtBu/HOtBu transforms it to the acetal 13. The epoxybenzochromenes 8, 9, and 11 rearrange on heating at 110°C to give the epoxyxanthene derivatives 16−18.

Keywords: Allenes / Amines / Boranes / Cycloadditions / Eliminations / Strained molecules 3-Bromo-1-methyl-1,2,5,6-tetrahydropyridine(N−B)borane (7) was prepared from 3-bromopyridine by conversion to 3-bromo-1-methylpyridinium iodide, hydrogenation of the latter with sodium tetrahydroborate and treatment of the resulting 3-bromo-1-methyl-1,2,5,6-tetrahydropyridine (6) with borane−dimethyl sulfide. Whereas no trapping product of the possible intermediate 1-methyl-1-azacyclohexa-2,3-diene (4) could be observed on treatment of 6 with potassium tert-but-

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