765906-69-2Relevant academic research and scientific papers
Br?nsted acid-promoted cyclizations of siloxy alkynes with unactivated arenes, alkenes, and alkynes
Zhang, Liming,Sun, Jianwei,Kozmin, Sergey A.
, p. 11371 - 11380 (2007/10/03)
In this article, we describe the development of a general concept for the development of new carbon-carbon bond-forming processes, which is based on Br?nsted acid-mediated activation of a siloxy alkyne, followed by efficient interception of the resulting highly reactive ketenium ion by unactivated arenes, alkenes or alkynes. We found that trifluoromethane sulfonimide (HNTf2) proved to be a superior promoter of these reactions compared to a range of other Br?nsted acids. This finding could be attributed to a high acidity of HNTf2 in aprotic organic solvents combined with a low nucleophilicity of the NTf2- anion. Depending on the nature of the nucleophile, the carbocyclizations proceeded either via 6-endo-dig or 5-endo-dig manifolds. In the case of 1-siloxy-1,5-diynes, the cyclizations occurred with a concomitant halide abstraction or arylation.
Au- and Pt-catalyzed cycloisomerizations of 1,5-enynes to cyclohexadienes with a broad alkyne scope
Sun, Jianwei,Conley, Matthew P.,Zhang, Liming,Kozmin, Sergey A.
, p. 9705 - 9710 (2007/10/03)
We describe the development of gold- and platinum-catalyzed cycloisomerizations of 1,5-enynes. This catalytic process displays a wide alkyne scope and furnishes a range of highly functionalized 1,4- and 1,3-cyclohexadienes. In the case of 1-siloxy-1-yne-5-enes, the reactions are efficiently catalyzed by AuCl (1 mol %) at ambient temperature to afford siloxy cyclohexadienes or the corresponding 1,2- and 1,3-cyclohexenones upon subsequent protodesilylation. We propose that the reaction proceeds via a novel mechanism involving a series of 1,2-alkyl shifts. Elucidation of this unusual reaction mechanism enabled us, in turn, to significantly expand the scope of the cycloisomerization by incorporation of a quaternary center at the C(3) position of the enyne. Indeed, we established that PtCl2 (5 mol %) efficiently catalyzed the cycloisomerizations of 1,5-enynes containing terminal, internal, and arene-conjugated alkynes. Since a variety of 1,5-enynes are readily accessible, the cycloisomerization provides a rapid approach to a wide range of highy substituted cyclohexadienes for many subsequent synthetic applications.
Gold-catalyzed cycloisomerization of siloxy enynes to cyclohexadienes
Zhang, Liming,Kozmin, Sergey A.
, p. 11806 - 11807 (2007/10/03)
We have described the first Au-catalyzed cycloisomerization of 1-siloxy-5-en-1-ynes. The reaction is efficiently catalyzed by AuCl (1 mol %) to afford siloxy cyclohexadienes, which can be readily converted to the corresponding 1,2- and 1,3-cyclohexenones. The catalytic process displays a broad substrate scope and exceedingly mild reaction conditions (30 min, 20 °C). The presence of a siloxy alkyne moiety is crucial for enabling the skeletal reorganization process, which is postulated to proceed via a novel reaction mechanism involving a cascade of 1,2-alkyl migrations. Copyright
Bronsted acid-promoted cyclizations of siloxyalkynes with arenes and alkenes
Zhang, Liming,Kozmin, Sergey A.
, p. 10204 - 10205 (2007/10/03)
We have described the first Bronsted acid-mediated cyclizations of siloxyalkynes with simple arenes and alkenes to afford substituted tetralone and cyclohexenone derivatives. The most notable aspect of the carbocyclizations involving siloxyalkynes is the ability to employ a range of substrates that are not restricted to those containing electron-rich arenes and alkenes. The key mechanistic feature of the reaction is the generation of a highly reactive ketenium ion upon protonation of siloxyalkyne. We believe that the low nucleophilicty of the counteranion is crucial for enabling the formation and effective interception of this highly reactive intermediate. Copyright
