Qiang Wang

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The asymmetric Pictet–Spengler reaction (PSR) with aldehydes is well known. However, PSR involving ketones as electrophilic partners is far-less developed. We report herein the first examples of catalytic enantioselective PSR of tryptamines with α-ketoamides. A new class of easily accessible prolyl-urea organocatalysts bearing a single H-bond donor function catalyzes the title reaction to afford 1,1-disubstituted tetrahydro-β-carbolines in excellent yields and enantioselectivities. The kinetic isotope effect using C2-deuterium-labelled tryptamine indicates that the rearomatization of the pentahydro-β-carbolinium ion intermediate might be the rate- and the enantioselectivity-determining step.

2022

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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.

2022

Copper‐Catalyzed Aza‐Sonogashira Cross‐Coupling to Ynimines: Development and Application to the Synthesis of Heterocycles

Rémi Hugo Lavernhe, Qiang Wang, Jieping Zhu

Nitrogen substituted alkynes such as ynamines and ynamides are versatile synthetic building blocks in organic chemistry. Ynimines bearing additional nucleophilic and electrophilic centers relative to ynamines and ynamides are expected to have high synthetic potential. However, their chemical reactivity remains unexplored due mainly to the lack of synthetic accessibility. We report herein a versatile Cu-catalyzed synthesis of ynimines from readily available O-acetyl ketoximes and terminal alkynes. A wide range of O-acetyl ketoximes derived from diaryl ketones, aryl alkyl ketones and dialkyl ketones undergo cross-coupling with a diverse set of terminal alkynes to afford the ynimines in good to excellent isolated yields. An unprecedented [5+1] heteroannulation reaction exploiting the reactivity of the in situ generated ynimine is subsequently developed for the synthesis of medicinally important heterocycles including isoquinolines, aza-indoles, aza-benzofurans, aza-benzothiophenes and carbolines. We anticipate that this robust synthesis of ynimines would open an avenue for the exploration of this functionally rich building block .

2021