Higher-order cyclopropenimine superbases: Direct neutral brønsted base catalyzed michael reactions with α-aryl esters

Eric D. Nacsa, Tristan H. Lambert

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

The synthesis and characterization of six new classes of higher-order superbases, including five that incorporate cyclopropenimine functionality, has been achieved. We propose a nomenclature that designates these as the CG2, GC2, PC3, PC1, C3, and GP2 classes of superbases. The pKBH+ values were measured to be between 29.0 and 35.6 in acetonitrile. Linear correlations of ten superbase basicities vs that of their substituents demonstrated the insulating effect of the cyclopropenimine core. The molecular structures of several of these materials were obtained by single-crystal X-ray analysis, revealing interesting aspects of conformational bias and noncovalent organization. The types of superbasic cores and substituents were each reliably shown to affect selectivity for deprotonation over alkylation. Higher-order cyclopropenimine and guanidine superbase stability to hydrolysis was found to correlate to basicity. Finally, a GC2 base was found to catalyze conjugate additions of α-aryl ester pronucleophiles, representing the first report of a neutral Brønsted base to catalyze such reactions.

Original languageEnglish (US)
Pages (from-to)10246-10253
Number of pages8
JournalJournal of the American Chemical Society
Volume137
Issue number32
DOIs
StatePublished - Aug 19 2015

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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