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

Abstract

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.

Generation of Donor/Donor Copper Carbenes through Copper-Catalyzed Diyne Cyclization: Enantioselective and Divergent Synthesis of Chiral Polycyclic Pyrroles

“…On the basis of the above experimental results and previous protocols on ynamide chemistry, a plausible mechanism for the synthesis of tetracyclic pyrrole 2a and tricyclic pyrrole 4g is illustrated in Scheme (path a). Initially, electron-rich ynamide moiety attacks the [Cu]-activated another C–C triple of 1a to afford the vinyl copper intermediate A , or its resonance form B . Subsequent [1,4]-H shift , generates the donor/donor copper carbene intermediate C .…”

The Aryne Ene Reaction

“…As part of a wider study into the ene reaction of allenes, Lee and co-workers reported an intermolecular aryne ene reaction between linear silylallene 81a and o -silylaryl triflate 20 to afford TMS-alkyne 83a (Scheme 18b ). 41 The silyl group significantly weakens the α-allenic C(sp 2 )–H bond, which was found to be key to accessing this mode of reactivity in preference to engaging the allylic C(sp 3 )–H bond, as observed in cases of non-silylated substrates with alternative enophiles.…”

Efficient Heterogeneous Copper-Catalyzed Alder-Ene Reaction of Allenynamides to Pyrrolines

“…The Alder-ene reaction has been recognized as a powerful synthetic tool for the rapid construction of C–C bonds with high atom economy and efficiency . Since the seminal work by Trost on the palladium-catalyzed intramolecular ene reactions of 1,6-enynes, the ene-type cycloisomerizations of various 1, n -unsaturated systems, such as dienes, enynes, triynes, and enallenes, have been reported. However, the corresponding Alder-ene reaction of allenynes is less investigated. , In 2002, Brummond reported the rhodium­(I)-catalyzed formal Alder-ene-type reaction of 1,6-allenynes for stereoselective synthesis of cross-conjugated trienes (Scheme a) .…”