The development of gold(I)-catalyzed intermolecular carbo- and hetero-cycloadditions of alkynes and allenes has been more challenging than their intramolecular counterparts. Here we review, with a mechanistic perspective, the most fundamental intermolecular cycloadditions of alkynes and allenes with alkenes.
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http://dx.doi.org/10.1002/asia.201402395 | DOI Listing |
Molecules
November 2024
School of Chemistry, University College Dublin, Belfield, D04 V1W8 Dublin 4, Ireland.
Alkynylallenes offer the varied reactivity patterns of two different multiple bond linkages either separately or in concert. Initially, a short overview of their syntheses, structures, rearrangement mechanisms and synthetic utility, especially when treated with transition metal reagents such as gold(I), silver(I), platinum metals or metal carbonyls, is presented. Subsequently, we focus on the particular case of 1,2-dien-5-ynes (propargylallenes), whereby the shortness of the single atom bridge, and the consequent proximity of the allenyl and alkynyl moieties, facilitates metal-mediated interactions between them.
View Article and Find Full Text PDFJ Am Chem Soc
December 2024
Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States.
The cumulated π system of a nonsymmetric allene contains three distinct unsaturated carbons that imbue it with unique reactivity toward radicals as compared to its alkene and alkyne counterparts. Despite the synthetic potential of these versatile building blocks, electrochemical transformations of allenes have been historically underexplored. Myriad strategies for easy access to allenes, coupled with the resurgence of interest in sustainable oxidative transformations of hydrocarbons, prompted our efforts to conduct an in-depth investigation of a rare example of an electrochemical TEMPO-mediated allene dioxygenation.
View Article and Find Full Text PDFPhys Chem Chem Phys
December 2024
Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Chile.
This paper presents a theoretical study on the distinguishable regiodivergent C-C Myers-Saito and C-C Schmittel routes of benzannelated enyne-allene cycloaromatizations, in which substitutions on the terminal alkyne by alkyl (-CH, -CHCH, -CH(CH) and -C(CH)) and aryl (-CH and -CH(CH)) groups were included. Mechanistic differences were found between substituents attached to alkynes with and without α-H, whereas in the former the Schmittel cyclization proceeds together with 1,8-H migration, in the latter it does so as the sole primitive event. It was also observed that bulky substituents preferentially favor the C-C Schmittel route, and the statistical prediction of regioselectivity is greatly affected when the ratio of accessible vibrational microstates of the transition states is included, especially in highly competing routes, , ΔΔ → 0.
View Article and Find Full Text PDFOrg Lett
December 2024
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 211800, China.
The Pd-catalyzed reaction of 1-(2-iodophenyl)-3-arylprop-2-yn-1-ones with benzene-tethered furan-ynes produces novel fused hexacyclic indenone-furan scaffolds, while the reaction with propargyl furfuryl ethers affords the pentacyclic indenone-spirodifuran system. The thiophene-containing alkynes also proceed by similar transformations. A mechanism involving the Pd-catalyzed coupling and propargylic Alder-ene reaction to generate the indenone-allene intermediate, followed by an intramolecular furan/thiophene-participated inverse electron-demand Diels-Alder reaction, is proposed.
View Article and Find Full Text PDFOrg Lett
December 2024
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China.
A cobalt-catalyzed intramolecular [4 + 2] cycloaddition of cyclopropyl (CP)-capped dienes with ynes/enes/allene was reported, providing an efficient method toward a spiro[2.5]octene ring system found in natural products, such as illudin. The [4 + 2] cycloadducts can be converted into other compounds via CP chemistry.
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