Catalytic asymmetric diels-alder reaction of 2’-Hydroxychalcone as a dienophile with VANOL-borate ester complex

Title : Catalytic asymmetric diels-alder reaction of 2’-Hydroxychalcone as a dienophile with VANOL-borate ester complex

Abstract:

A large number of natural products have been isolated from various Moraceous and related plants, in which more than forty classes of prenylflavonoid and related Diels-Alder (DA)-type natural products have been characterized. Due to their potent biological activities, including anti-inflammatory, anti-anticancer, anti-HIV and anti-malarial, and so on, the Diels-Alder natural products are intriguing synthetic targets. One of the most effective method for the syntheses of these DA-type natural products is the Diels-Alder cycloaddition of substituted chalcones and diene substrates. In our previous studies, an efficient method for the asymmetric Diels-Alder cycloaddition of 2’-hydroxychalcones with acyclic or cyclic dienes has been successfully developed. The Diels-Alder cycloaddition is mediated by a chiral boron complex with VANOL, affording the corresponding products in high yields and with excellent diastereo- and enantioselectivities. It's worth stating that the chiral VANOL/BH3/AcOH catalyst complex was used in stoichiometric amount (1.2-2.5 equivalent). Herein, we reported an efficient catalytic asymmetric Diels-Alder cycloaddition of 2’-hydroxychalcone and its derivatives using catalytic amount in situ generated chiral R-VANOL-Borate complex. To probe the effect of catalyst loading on the reaction yield and enantioselectivity, different equivalents of LA4 were screened under the above optimal conditions (PhCF3, 100 oC). The result suggested that 10 mol % of B(OPh)3/R-VANOL complex is sufficient to promote this asymmetric reaction efficiently. A bright orange color change was observed when the borate catalyst and 2’-hydroxychalcone were combined, indicating the potential generation of an active borate complex that has been previously confirmed by single X-ray crystal structure analysis and density functional theory calculations.

Audience Takeaway Notes:

• A method for catalytic asymmetric synthetic methodology and its application.
• The reactivity and enantioselectivity depend on the in situ generated chiral boron complexes.
• The researchers will be able to apply this catalytic approach in their scientific research.

Biography:

Dr. Li studied Chemistry at the Zhengzhou University, China and graduated as MS in 2008. She then joined the research group of Prof. Lei at the National Institute of Biological Science (NIBS), Beijing & Tianjin University, Tianjin, China. She received her PhD degree in 2014 and joined the Tianjin Key Laboratory for Prevention and Control of Occupational and Environmental Hazards, China. She was recognized as an Associate Professor in 2019. Her specific research interests include the following: Development of new catalytic reactions for the efficient construction of substituted cyclohexanes, total synthesis of structurally complex and bioactive natural products, exploring the mechanism and target of action of anti-hypoxia active natural small molecules.