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Abstract We describe novel amine‐mediated transformation of alkynyl ketones and amides to generate 2‐methylene‐2H‐pyrans, substituted 3‐hydroxy‐9H‐fluoren‐9‐ones, and amine‐incorporated arenes. These cascade processes are initiated by conjugate addition of secondary amine followed by hydrolysis of the enamine/vinylogous amide intermediates. The product distribution is highly sensitive to the steric and electronic effects of the substituents on both the alkyne moieties, the tether structure connecting them, and the nature of the amine. Alkynyl amide participates in the Alder‐ene reaction favorably to generate more reactive allene amide that reacts with amine to generate amine‐incorporated arene products. These metal‐free cascade reactions are a useful synthetic method that can be exploited for the construction of various hetero‐ and carbocyclic systems. 

Abstract The cycloisomerization of alkyne‐tetheredN‐benzoyloxycarbamates to 2‐(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5‐exo‐alkyne carboxyamidation and concomitant alkene isomerization. PtCl₂/CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl₃(5 mol%, CH₃CN, 100 °C) promotes carboxyamidation effectively but a cocatalyst is required for the exocyclic alkene isomerization. Thus, a two‐step one‐pot protocol has been developed for a broader reaction scope, which involves FeCl₃‐catalyzed carboxyamidation and base‐induced alkene isomerization. Crossover experiments suggest that these reactions proceed mainly through a mechanism involving acylnitrenoid intermediates rather than carbenoid intermediates. 

Abstract A new [4+2] cycloaddition of allenyne‐alkyne is developed. The reaction is believed to proceed with forming an α,3‐dehydrotoluene intermediate. This species behaves as a σπ‐diradical to react with a hydrogen atom donor, whereas it displays a zwitterionic reactivity toward weak nucleophiles. The efficiency of trapping α,3‐dehydrotoluene depends not only on its substituents but also the trapping agents. Notable features of the reaction are the activating role of the extra alkyne of the 1,3‐diyne that reacts with the allenyne moiety and the opposite mode of trapping with oxygen and nitrogen nucleophiles. Oxygen nucleophiles result in the oxygen‐end incorporation at the benzylic position of the α,3‐dehydrotoluene, whereas with amine nucleophiles the nitrogen‐end is incorporated into the aromatic core. Relying on the allenyne‐alkyne cycloaddition as an enabling strategy, a concise total synthesis of phosphodiesterase‐4 inhibitory selaginpulvilin A is realized. 

Abstract We describe Pt(II)- and Fe(III)-catalyzed iminocarboxylations of oxime esters conjugated with 1,3-enyne and an ortho-alkynylarene moiety, followed by a spontaneous O→N acyl migration of the enol carboxylate intermediate to generate N-acyl pyrroles and isoindoles. The reaction scope for pyrrole synthesis is general, whereas the formation of isoindoles has a relatively narrow scope because of their instability.