Taming the radical cation intermediate enabled one-step access to structurally diverse lignans

Abstract

Lignans, in spite of their structural diversity, are all biosynthetically derived from coniferyl alcohol. We report herein a divergent synthesis of lignans from biomass-derived monolignols in a short synthetic sequence. Blue LED irradiation of a dichloromethane solution of dicinnamyl ether derivatives in the presence of Cu(TFA)2, an alcohol (2.0 equiv) and a catalytic amount of Fukuzumi’s salt affords the C7-alkoxylated aryltetralin cyclic ethers. Increasing the amount of alcohol under otherwise identical conditions diverts the reaction course to furnish the C7,C7’-dialkoxylated dibenzyltetrahydrofurans, while replacing Cu(TFA)2 with diphenyl disulfide (PhSSPh) provides selectively the C7-monoalkoxylated dibenzyltetrahydrofurans. Aza-, thia- and carba-analogues of lignans are equally accessible by simply changing the tethering atom of the allylic alcohols. Concise total syntheses of aglacins A, E, F, brassilignan, and dehydrodimethylconidendrin are documented featuring these transformations.

Macrophage-Inspired Degradation-Activation System Enables Ultrasensitive Multicolor Detection of Haloacetic Acids via Janus Perovskite Halide Exchange

“…Once exposed to UVC light, MTBE can be photodegraded to a tert -butyl cation intermediate in an acid medium, which is rather stable for hyperconjugation . In fact, the application potential of cation intermediates in synthetic conversion has been reported . Thus, the stable tert -butyl cation intermediate becomes the best accepting group for the free halogen group, and new C–X bonds can be formed.…”

“…39 In fact, the application potential of cation intermediates in synthetic conversion has been reported. 40 Thus, the stable tert-butyl cation intermediate becomes the best accepting group for the free halogen group, and new C−X bonds can be formed. To sum up, the possible mechanisms of photolysis reaction and perovskite halide exchange are deduced, as shown in Figure 4a.…”

Cu(ii) salts as terminal oxidants in visible-light photochemical oxidation reactions

“…Subsequently, Zhu and coworkers exploited Cu( ii ) oxidants in a photocatalytic synthesis of lignans, a class of natural products derived from coniferyl alcohol. 17 Aryltetralin cyclic ethers could be synthesized from dimeric or psuedodimeric-cinnamyl ethers in the presence of a highly oxidizing photocatalyst, Cu(TFA) 2 as a terminal oxidant, and MeOH as a nucleophile (Scheme 7). The authors proposed that the reaction cascade is initiated by the oxidation of styrene 22 by the excited-state photocatalyst, which undergoes cyclization to afford distonic 1,4 radical cation 24 .…”

Combining the best of both worlds: radical-based divergent total synthesis

“…(Zhu, 2022) [103]: Lignans are structurally diverse natural compounds generated biosynthetically by the oxidative dimerization of phenylpropanoids [104]. Despite the wide oxidative diversity, classic lignans bearing a C8-C8' bond can be biosynthetically traced back to coniferyl alcohol (Scheme 18).…”