Kumar R, Padhy SR, Balaraman E. Cobalt-Catalyzed Divergence in C(sp
3)-H Functionalization of 9
H-Fluorene: A Streamlined Approach Utilizing Alcohols.
J Org Chem 2024;
89:15103-15116. [PMID:
39378241 DOI:
10.1021/acs.joc.4c01887]
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Abstract
Sustainable chemical production demands the creation of innovative catalysts and catalytic technologies. While the development of coherent and robust catalytic systems using earth-abundant transition metals is essential, it remains a significant challenge. Herein, an expedient divergence strategy for tandem dehydrogenative C(sp3)-H alkylation and cyclization reactions of 9H-fluorene using a newly developed N,N-bidentate cobalt catalytic system is developed. This method capitalizes on the use of abundant and readily accessible alcohol. Demonstrating wide-ranging applicability, the catalytic protocol successfully integrated a diverse array of fluorenes and alcohols. This includes benzylic, heteroaromatic, and aliphatic primary and secondary alcohols, amassing a total of 75 distinct examples. When applied to sterically bulky alcohols, the reaction preferentially undergoes alkenylation, yielding a tetrasubstituted olefin as the main product. In the case of diols, the expected outcome is Dual-fluorescence at both terminal positions. This process leads to difluorination, followed by a cyclization step, culminating in the formation of a relatively unprecedented spiro compound. The scalability of this method has been validated through gram-scale synthesis. Control experiments have shed light on the reaction mechanism, indicating that it progresses through an unsaturated intermediate and adheres to the borrowing hydrogen pathway.
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