Abstract
Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis. These structures can be found in a wide range of polycyclic natural products and drug molecules. Here we report a Ti(Oi-Pr)4-promoted photoenolization/Diels–Alder (PEDA) reaction to construct hydroanthracenol and related polycyclic rings bearing all-carbon quaternary centers. This photolysis proceeds under mild conditions and generates a variety of photo-cycloaddition products in good reaction efficiency and stereoselectivity (48 examples), and has been successfully used in the construction of core skeleton of oncocalyxones, tetracycline and pleurotin. It also provides a reliable method for the late-stage modification of natural products bearing enone groups, such as steroids. The total synthesis of oncocalyxone B was successfully achieved using this PEDA approach.
Highlights
Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis
We noticed a group of polyketides with all-carbon quaternary centers within the core anthracenols or anthraquinones, such as the newly isolated A-74528 [3]5, 6 and JBIR-85 [4]7, as well as the antibiotics pleurotin [5]8–13 and oncocalyxone B [6]14, 15
When we tested the photoreaction conditions of Nicolaou et al.48, we found that ultraviolet (UV) irradiation of a solution of 7 (1.0 equivalent) and 8 (6.0 equiv.) in degassed toluene for 2 h led to only trace amounts of hetero-cycloaddition product 11 and no formation of the desired cycloaddition product (Table 1, entry 1)
Summary
Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis. We report a Ti(Oi-Pr)4-promoted photoenolization/Diels–Alder (PEDA) reaction to construct hydroanthracenol and related polycyclic rings bearing all-carbon quaternary centers This photolysis proceeds under mild conditions and generates a variety of photo-cycloaddition products in good reaction efficiency and stereoselectivity (48 examples), and has been successfully used in the construction of core skeleton of oncocalyxones, tetracycline and pleurotin. Since our research group is devoted to the synthesis of bioactive natural products, we decided to explore new approaches to prepare the core structure IV in a stereo-controlled way, which can serve as a common precursor for the synthesis of others (I–III) with higher oxidation states by simple oxidations We hope this method can be effectively utilized in the synthesis of 3–6 and their derivatives for biological and drug discovery studies. As far as the intermolecular PEDA reactions are concerned, we realized a
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
