Asymmetric Total Synthesis of Dragonbloodins A1 and A2

Abstract

The first asymmetric total synthesis of dragonbloodins A1 and A2, a pair of unprecedented chalcone-flavan heterotrimmers, has been achieved through a series of rationally designed or bioinspired transformations. Key elements of the synthesis include a highly efficient heterotrimerization reaction to assemble the two chalcone units and one flavan unit in one pot and a tandem oxidative dearomatization/cyclization/oxygenation reaction to forge the polycyclic core of dragonbloodins A1 and A2. The present synthesis unambiguously confirms the biogenetic relationship and absolute stereochemistry of dragonbloodins A1 and A2.

Asymmetric hydrogenation and transfer hydrogenation in the enantioselective synthesis of flavonoids

“…The cyclization of 1,3-diarylpropan-1-ols is a well-established method for the synthesis of flavans. 98–100 In this context, the enantioselective reduction of dihydrochalcones provides access to the corresponding enantioenriched alcohols, leading to the asymmetric synthesis of flavans. This approach was employed by Merck's group in 2017 for the synthesis of flavan ( R )- 200 (Scheme 47).…”

Ru(II)-Catalyzed Asymmetric Transfer Hydrogenation of Chalcones in Water: Application to the Enantioselective Synthesis of Flavans BW683C and Tephrowatsin E

“…These chiral alcohols are bioactive natural products also isolated from plants that produce flavans, suggesting a biosynthetic relationship . Furthermore, 1,3-diarylpropan-1-ols bearing a 2-OH group at ring B are known as key synthetic intermediates for the synthesis of flavans through Mitsunobu cyclization. , Thus, we hypothesized that the one-pot CC/CO reduction of chalcones through a Ru-catalyzed ATH could stand out as a convenient alternative for the preparation of these intermediates, allowing the enantioselective synthesis of flavans in two steps from readily accessible substrates (Scheme c).…”

Enantioselective intermolecular [2 + 2] photocycloadditions of vinylazaarenes with triplet-state electron-deficient olefins

“…1(c)). However, in such a disperse reaction system, the highly reactivity of triplet-state olefins would have a considerable probability to directly experience homo-dimerization with the parent olefins [26,27] as well as to react with the free olefins. Exploration of the viability of this scenario therefore constitutes a meaningful but formidable task.…”