Allene Trifunctionalization via Amidyl Radical Cyclization and TEMPO Trapping

Radical-mediated trifunctionalizations of allenes are virtually unknown, in contrast to well-studied radical difunctionalizations of alkenes and alkynes. In this article, we describe a light-promoted reaction that transforms all three allene carbons to new carbon–heteroatom bonds in one pot with no expensive transition-metal catalyst. Formation of an electron donor-acceptor complex between an electron-deficient aryl and K2CO3, followed by photochemical generation of an amidyl radical and cyclization, yields a vinyl radical that can be trapped by TEMPO to ultimately furnish the product. Insights into the impact of the allene substitution pattern, radical source, and donor are presented, along with studies to unravel the mechanism of this unusual transformation.