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Published on: February 7, 2019
Organocatalytic Atroposelective Formal C(sp2)-H Alk(en)ylation: Enantioselective Synthesis of Class 2 Atropisomeric
Subhajit Mondal1, Santanu Mukherjee1
1Department of Organic Chemistry, Indian Institute of Science, Bangalore 560012, India.
Abstract:
The borderline rotational barrier of class 2 atropisomeric quinones makes their enantioselective synthesis challenging. Herein we report the first catalytic atroposelective formal C(sp2)-H methylation and alkenylation of atropisomerically labile 2-aryl (naphtho)quinones. Employing nitroalkanes as alk(en)ylating agents, these reactions are catalyzed by a bifunctional tertiary aminourea derivative and proceed via dynamic kinetic resolution (DKR). The resulting 2-aryl 3-alk(en)yl quinones exhibit rotational barriers characteristic of class 2 atropisomers and are isolated in good to excellent yields with generally exclusive (E)-selectivity and high enantioselectivity. The synthetic utility of 2-aryl 3-alk(en)yl quinones is showcased through several stereospecific downstream transformations. Mechanistic studies reveal that the byproduct nitrite acts as the terminal oxidant in the alkenylation pathway. To the best of our knowledge, this is the first time nitroalkanes have been shown to function as alkenylating agents, at least in an enantioselective transformation.
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