Herein, we report the nickel-catalyzed cascade CÀ O bond cleavage/cyclization of ortho-alkynylphenyl ester to construct a 3-acylbenzo[b]furan skeleton. As a result of reaction condition screening, the Ni(0)/IAd (1,3-Di(1-adamantyl)imidazole-2ylidene) system was found to be optimal for catalytic conversion. Interestingly, the reaction exclusively gives 3acylbenzo[b]furan instead of a decarbonylated product fre-quently observed in reactions mediated by acyl-nickel species. The catalyst loadings could be reduced to 5-10 mol %. We demonstrated the synthesis of a variety of functionalized 3acylbenzofuran derivatives. We conducted stoichiometric study of nickel complexes as well as density functional theory (DFT) calculations to support a possible reaction mechanism.
We herein describe a cobalt/Xantphos-catalyzed regioselective addition of simple alkenes to acetophenone derivatives, affording branched homoallylic alcohols in high yields with perfect branch selectivities. The intermediate of the reaction would be a nucleophilic allylcobalt(I) species generated via cleavage of the low reactive allylic C(sp3)–H bond of simple terminal alkenes.
In the presence of a catalytic amount of cobalt(II) acetylacetonate/Xantphos in combination with trimethylaluminum, various ketoalkenes underwent an intramolecular cyclization reaction triggered by cleavage of the allylic C(sp3)−H bond, affording carbocyclic compounds with high regio‐ and diastereoselectivity. Mono‐, bi‐, and tricarbocyclic compounds were produced in good yields. One of the products thus obtained was derivatized into tramadol in four simple steps. Notably, these intramolecular cyclizations took place in the absence of a gem‐disubstituent on the tethered carbon chain (without the Thorpe‐Ingold effect).
The front cover picture was provided by Tsuyoshi Mita and co‐authors. They revealed that various ketoalkenes underwent a Co‐catalyzed intramolecular cyclization reaction triggered by cleavage of the allylic C(sp3)–H bond, affording carbocyclic compounds with high regio‐ and diastereoselectivity. This picture represents that ketoalkenes are automatically converted to tramadol, a novel pain drug, by a “Co‐Xantphos factory”. This paper is dedicated to our scientific hero, Professor Eric N. Jacobsen on the occasion of his 60th birthday. Further details of this work can be found in the communication on pages 1275–1280 (T. Mita, M. Uchiyama, Y. Sato, Adv. Synth. Catal. 2020, 362, 1275–1280; DOI: 10.1002/adsc.201901533).).
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