Synthesis of unsubstituted derivatives and kinetic study of their equilibration to cyclopropanone. We theorized that establishing the equilibrium between 1-sulfonylcyclopropanols and cyclopropanones would be key to subsequent reaction development efforts using these substrates. To do so, we sought to access electronically and sterically differentiated achiral sulfonylcyclopropanols (2) to evaluate the effect of the leaving group on such an equilibrium (Scheme 2). Prior to this work, only the phenylsulfonyl-(R = Ph, 2a) and p-tolylsulfonyl-(R = 4-Me-C6H4) substituted achiral sulfonylcyclopropanols had been reported by Chen in moderate yields, and the procedure required distillation and isolation of hemiketal intermediate as well as recrystallization of the final product. Building on this approach, we first optimized a practical and general one-pot protocol leading to variously substituted 1sulfonylcyclopropanols 2a-2n in moderate to excellent yields (Scheme 2a). Starting from commercially available (1ethoxycyclopropoxy)trimethylsilane, acid-mediated cleavage of the silyl group rapidly affords a solution of hemiketal 1, which is directly treated with the corresponding sodium sulfinate salt in presence of formic acid and water at room temperature. Using these conditions, cyclopropanone precursors were directly obtained in pure form after aqueous workup without the need for isolation of 1, and the procedure was applied on gram-scale with similar efficiency. 11 With these substrates in hand, we employed a novel pyrazole substitution reaction leading to adduct 3 to evaluate the relative rate of conversion of the sulfonylcyclopropanols to cyclopropanones (Scheme 2b). Such a trapping reaction was found to be particularly clean and occurred at a rate that was easy to follow by NMR at room temperature. Considering the highly strained and energetic character of cyclopropanone, it is anticipated that the initial equilibrium leading to its formation is rate-limiting of the overall process. Hence, the relative rates measured for each precursor 2 in this reaction should be indicative of their relative propensity to equilibrate to cyclopropanone. In a general manner, electronpoor sulfinate adducts were found to react faster (e.g. see , presumably due to the increased electronic stabilization and reduced nucleophilicity of the corresponding sulfinate anion leaving group RSO2HNEt3 (Scheme 2b, top). Moreover, evaluation of alkylsulfinic acid adducts 2i-2m enabled an assessment of the effect of steric hindrance on the sulfonylcyclopropanol's propensity to equilibrate to cyclopropanone, where encumbered substrates (e.g. 2m) were generally found to be more reactive (Scheme 2b, bottom). This is likely due to the fact that sterically congested sulfonylcyclopropanols benefit from a greater torsional (Pitzer) strain release during the rate-limiting α-elimination process, even though ring (Baeyer) strain is significantly increased in all cases. These observed trends are further reinforced by the fact that particularly hindered 2h or electron-poor 2n 1-sulfonylcyclopropanols could not be obtained using our optimized procedure, as they were found to be too unstable to isolation and only led to decomposition, likely due to spontaneous equilibration to cyclopropanone. The results of the kinetics observed using 2a-2n highlight the modular nature of 1-sulfonylcyclopropanols as cyclopropanone equivalents, where a wide spectrum of equilibration rates could be obtained through simple modification of the sulfonyl group. Scheme 2. Synthesis of unsubstituted 1-sulfonylcyclopropanols (a) a and structure-reactivity relationship in a pyrazole substitution (b) b a Isolated yields. b NMR yields for each timepoint were determined by 1 H NMR analysis using 1,3,5-trimethoxybenzene as standard.