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Relevant academic research and scientific papers

Synthesis of Benzodihydrofurans by Asymmetric C?H Insertion Reactions of Donor/Donor Rhodium Carbenes

Metal carbenes appended with two electron-donating groups, known as “donor/donor” carbenes, undergo diastereo- and enantioselective rhodium-catalyzed C?H insertion reactions with ether substrates to form benzodihydrofurans. Unlike the reactions of metal carbenes with electron-withdrawing groups attached, the attenuated electrophilicity enables these reactions to be conducted in Lewis basic solvents (e.g., acetonitrile) and in the presence of water. The diazo precursors for these species are prepared in situ from hydrazone using a mild and chemoselective oxidant (MnO2). Although this sequence often can be performed in one-pot, control experiments have elucidated why a “two-pot” process is often more efficient. A thorough screening of achiral catalysts demonstrated that sterically encumbered catalysts are optimal for diastereoselective reactions. Although efficient insertion into allylic and propargylic C?H bonds is observed, competing dipolar cycloaddition processes are noted for some substrates. The full substrate scope of this useful method of benzodihydrofuran synthesis, mechanisms of side reactions, and computational support for the origins of stereoselectivity are described.

Dehydrative condensation of carbonyls with non-acidic methylenes enabled by light: Synthesis of benzofurans

Condensation of carbonyls with non-acidic methylenes such as those adjacent to heteroatoms and allylic types to generate CC bonds is challenging but highly desirable. Inventing novel methods that can accomplish such condensations can enrich synthetic chemists' toolbox. Herein, we report a simple, clean, and high yielding protocol promoted by light to achieve condensation of non-acidic methylenes with carbonyls. As examples to demonstrate the power of this methodology, one class of ubiquitous and highly important heterocycles, i.e. benzofurans, were synthesized with broad functional group compatibility. Furthermore, intermolecular condensations were also briefly investigated.

Enantioselective intramolecular C-H insertion reactions of donor-donor metal carbenoids

The first asymmetric insertion reactions of donor-donor carbenoids, i.e., those with no pendant electron-withdrawing groups, are reported. This process enables the synthesis of densely substituted benzodihydrofurans with high levels of enantio- and diaste