We devised a new method for asymmetric cyclopropanation
by employing
(S)-(thiolan-2-yl)diphenylmethanol benzyl ether as
an organocatalyst. Under optimal conditions, an in situ generated
sulfur ylide reacts with (E)-chalcones via a Johnson–Corey–Chaykovsky
reaction to afford a variety of cyclopropanes in excellent yields
and stereoselectivities. This strategy employs low-environmental-risk
reaction conditions and reusable catalysts. Hence, it is a green and
efficient method for constructing cyclopropane scaffolds.
This research account describes the development of chiral organocatalysts, focusing on diphenyl-2-pyrrolidinemethanol and its derivatives as valuable tools in asymmetric transformations. The research also includes the discovery of a novel anionic Si→C alkyl migration method, which has been developed into a one-pot procedure for synthesizing (E)-chalcones from hydroxyamide and N,N-diethylcarbamates. The findings underscore the potential of sulfide and silicon as valuable reagents for organic synthesis and emphasize the importance of exploring new reaction pathways and mechanisms to discover novel synthetic methods.
Clavicipitic acid, a communesin alkaloid precursor, has attracted significant attention due to its unique azepino [5,4,3-cd]indole framework. Herein, we report a novel biomimetic synthesis of clavicipitic acid diastereomers by utilizing a DDQ-mediated crossdehydrogenative coupling (CDC) reaction. The synthesis involves Suzuki coupling for the prenylation of a 4-bromotryptophan derivative, followed by an intramolecular CDC reaction to construct the azepinoindole core. The trans isomer was obtained as the major product, and the two diastereomers were separable. The CDC reaction conditions, including temperature, solvent, and protecting groups, were investigated, and a plausible mechanism for the observed diastereoselectivity was proposed.
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