Base-Promoted Direct Synthesis of Sulfinates from N-Sulfonyl­hydrazones under Metal-Free Conditions

Abstract

A base-promoted direct synthesis of sulfinates from N-sulfonylhydrazones is described. Various N-sulfonylhydrazones, derived from aldehydes and ketones, are converted into the corresponding sulfinates in moderate to good yields. This protocol possesses many advantages such as readily available and stable starting materials, broad substrate scope, and metal-free reaction conditions.

K2CO3-Catalyzed Rapid Conversion of N-Sulfonylhydrazones to Sulfinates

“…N-Tosylhydrazone obtained from fluorenone underwent a slow reaction to furnish sulfinate 3e in 56% yield after 1 h. Cyclopentanone-derived N-tosylhydrazone showed no reaction at 110 °C possibly due to a higher pK a value of the N−H proton. However, sulfinate 3f could be obtained in moderate yield (52%) when heated at higher temperature (150 °C) for 2 h. It is noteworthy that, in the previous reports, 18,19 Ntosylhydrazones derived from aliphatic carbonyl compounds could not be converted into corresponding sulfinates. Thus, the current condition further expands the substrate scope of this important transformation.…”

“…The conversion of N -sulfonylhydrazone to sulfinate proceeds intermolecularly, which was demonstrated by cross-over experiments in previous reports. 18 , 19 The proposed mechanism of the K 2 CO 3 -catalyzed conversion is depicted in Scheme 8 . The decomposition of N -sulfonylhydrazone 7 is triggered by the abstraction of N–H proton by K 2 CO 3 , generating deprotonated N -sulfonylhydrazone 8 and mild base KHCO 3 (inert under the reaction conditions).…”

“…The conversion of N-sulfonylhydrazone to sulfinate proceeds intermolecularly, which was demonstrated by crossover experiments in previous reports. 18,19 The proposed…”

“… 18 Adding to this development, in a very recent report, Wu et al have demonstrated that sulfinates could also be obtained selectively when N -tosylhydrazones are heated with a stoichiometric amount of diisopropylethyl amine in nitromethane at 90 °C ( Scheme 2 c). 19 Nonetheless, it is worth noting that, as per mechanism, the conversion of N -tosylhydrazone to the corresponding sulfinate should be catalytic with a base. However, unfortunately, the previous methods fail to give a complete conversion with a catalytic amount of base/promoter.…”

“…On the contrary, N -tosylhydrazones give corresponding sulfinates when heated with a stoichiometric amount of stabilized Wittig ylide in N , N ′-dimethylpropylene urea (DMPU) at elevated temperature under transition-metal-free conditions (Scheme b) . Adding to this development, in a very recent report, Wu et al have demonstrated that sulfinates could also be obtained selectively when N -tosylhydrazones are heated with a stoichiometric amount of diisopropylethyl amine in nitromethane at 90 °C (Scheme c) . Nonetheless, it is worth noting that, as per mechanism, the conversion of N -tosylhydrazone to the corresponding sulfinate should be catalytic with a base.…”