5 years ago

Cyclization of Ynamide-Tethered 1,3,8-Triynes

Cyclization of Ynamide-Tethered 1,3,8-Triynes
Peipei Xie, Yuanzhi Xia, Venkata R. Sabbasani, Hyunjin Lee, Daesung Lee
A facile thermal cyclization of ynamide-tethered 1,3,8-triynes to form a 3,5,6,7-tetrahydro-1H-pyrano[3,4-c]pyridine skeleton is described. Although the mechanism of this unusual reaction has yet to be defined, the formation of either a strained keteniminium or a biradical intermediate followed by a 1,5-hydride or -hydrogen shift is tentatively proposed as the key elementary steps in the reaction sequence. Appropriate electronic activation at the carbon center donating a hydride or hydrogen is crucial for successful cyclization. Zwitterionic or biradical: Thermal activation of ynamide-tethered 1,3,8-triynes induces a ring-closure to form a 3,5,6,7-tetrahydro-1H-pyrano[3,4-c]pyridine skeleton. A strained keteniminium or a biradical formation followed a 1,5-hydride or a hydrogen shift are the key elementary steps. An appropriate electronic activation at the hydrogen- or hydride-donating carbon, which leads to a stabilized oxonium or a radical species, is crucial for effective cyclization.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701781

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