Abstract
Pyrroles are structurally important heterocycles. However, the synthesis of polysubstituted pyrroles is often challenging. Here, we report a multicomponent, Ti-catalysed formal [2+2+1] reaction of alkynes and diazenes for the oxidative synthesis of penta- and trisubstituted pyrroles: a nitrenoid analogue to classical Pauson-Khand-type syntheses of cyclopentenones. Given the scarcity of early transition-metal redox catalysis, preliminary mechanistic studies are presented. Initial stoichiometric and kinetic studies indicate that the mechanism of this reaction proceeds through a formally TiII/TiIV redox catalytic cycle, in which an azatitanacyclobutene intermediate, resulting from [2+2] alkyne + Ti imido coupling, undergoes a second alkyne insertion followed by reductive elimination to yield pyrrole and a TiII species. The key component for catalytic turnover is the reoxidation of the TiII species to a TiIV imido via the disproportionation of an η2-diazene-TiII complex.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 63-68 |
| Number of pages | 6 |
| Journal | Nature Chemistry |
| Volume | 8 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 1 2016 |
Bibliographical note
Funding Information:Financial support was provided by the University of Minnesota (start-up funds). Equipment purchases for the Chemistry Department NMR facility were supported by a grant from the National Institutes of Health (S10OD011952) with matching funds from the University of Minnesota. The Bruker-AXS D8 Venture diffractometer was purchased through a grant from NSF/MRI (1224900) and the University of Minnesota.
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