Selective Sulfenylative Desulfonylation or Decarbalkoxylation of α-Sulfonyl Malonates with DABCO or Bu₃N: Reactivity and Conformational Analysis

Abstract

The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu₃N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO₂ and CO₂R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2∗ and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu₃N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate.

Keywords:

• Conformational analysis
• DABCO
• decarbalkoxylation–desulfonylation
• regioselectivity
• α-sulfonyl-malonates
• tributylamine

ACKNOWLEDGMENTS

The authors thank FAPEMIG (Fundação de Amparo à Pesquisa de Minas Gerais: EDT 479/07, CEX PPM III 0207/09) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) for financial support and fellowships.

Notes

^a,b,c After reaction with DABCO and addition of water, ^a MeSO₂SMe, ^b or PhSO₂SPh. ^c

^d All products were characterized by IR, NMR, and mass spectroscopy; isolated yields of products after column chromatography.