Palladium-catalyzed carbocyclization–cross-coupling reactions of two different allenic moieties: synthesis of 3-(buta-1,3-dienyl) carbazoles and mechanistic insights
作者:Benito Alcaide、Pedro Almendros、José M. Alonso、Israel Fernández
DOI:10.1039/c2cc32015k
日期:——
A palladium-catalyzed chemo-, regio- and stereoselective carbocyclizationâcross-coupling sequence of two different α-allenols to afford 3-(E-buta-1,3-dienyl) carbazoles is reported.
The room temperature radical cycloetherification/arylation cascade of allenols and diazoniumsalts has been accomplished via a combination of gold and photoredox catalysis to provide 2,3,4‐trisubstituted‐2,5‐dihydrofurans. The functionalized oxacycle formation sequence is chemo‐ and regioselective for the cycloetherification and for the position that bears the aryl moiety after the cross‐coupling.
The synergy between metal catalysis and radical chemistry allows to surpass previous limitations of the reactions between allenols and sulfonylating reagents. Considering that previous studies of the reactivity of the allenol moiety with sulfonylating reagents have been limited to addition and rearrangement reactions lacking cyclization, we decided to modify the protocol for achieving a catalytic
An Alternative to Precious Metals: Hg(ClO<sub>4</sub>)<sub>2</sub>·3H<sub>2</sub>O as a Cheap and Water-Tolerant Catalyst for the Cycloisomerization of Allenols
Hg(ClO4)(2)center dot 3H(2)O, a cheap, water-tolerant, and stable salt, catalyzes the cydoisomerization reaction or alpha-allenols to 2,5-dihydrofurans in an efficient and selective manner. The reaction is general and can be applied to differently functionalized substrates, including alkyl-substituted, aryl-substituted, enantiopure, and tertiary allenols. In addition, density functional theory (DFT) calculations were performed to obtain insight into various aspects of the controlled reactivity of a-allenols under mercury catalysis. They suggest a dual activation of the allenol by the Hg complex that drives the reaction to the chemoselective formation of 2,5-dihydrofurans.