Abstract
Reactions of methylenecycloalkanes 1a‐4a and cycloalkylidenecycloalkanes 11a–14a with sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane relative to the amount of SO~3~ as reactivity moderator. Methylenecyclooctane (1a), methylenecyclohexane (2a) and methylenecylopentane (3a) react with SO~3~ just like simple branched alkenes yielding quantitatively the corresponding β‐alkenesulfonic acids 1d‐3d. Reaction of methylenecyclobutane (4a) with 1.0 equiv. of SO~3~ at −60°C yields the β‐sultone 4b, which upon raising the temperature to 0°C, rearranges into γ‐sultone 6 and subsequently, slowly into δ‐sultone 9. Sulfonation of the cycloalkylidenecycloalkanes 11a‐13a with 1.0 equiv. of SO~3~ at −60°C leads to quantitative formation of the spiro‐β‐sultones 11b‐13b, respectively. After raising the temperature, these β‐sultones are converted into the corresponding β‐alkenesulfonic acids 11d‐13d, which are common reaction products in sulfonation of tetraalkylethenes.
Sulfonation of cyclopropylidenecyclopropane (14a) with SO~3~ at −60°C proceeds with rearrangement of one of the cyclopropyl groups to give quantitatively the spirocyclopropane‐γ‐sultone 15. Mechanisms for the formation of the various products are discussed.