Dearomatization Strategy Based On NHC Catalytic Indole Constructs Hydrocarbazolone Active Ingredient Skeleton

Objective: Compounds containing the hydrocarbazolones skeleton have a variety of biological activity,and there is a wide range of ruthenium plants.As a biologically active fragment,it has been used in the development of new drugs.At present,there is less research on 1,4a,9,9a-tetrahydro-4H-carbazole-4-one compounds.And the structure contains an indolyolin structure,thus the subject is proposed to construct 1,4a,9,9a-tetrahydro-4H-carbazole-4-one derivative.Methods: 3-phenylcrotonaldehyde compound with a NHC catalyst forme Homoenolates which can be oxidized with an external organic oxidant to acylazolium ions.The vinyl enolate intermediate is formed with an external base.Vinyl enolate intermediate then undergoes nucleophilic addition to 3-nitroindoles,eventually affording product 3.The structure could be confimed by 1H NMR,13 C NMR,HPLC,HRMS and X-ray single crystal and we would get the d.r.value,ee value,melting point and rotation of the target compounds 3.To further illustrate the generality of this protocol,we substituted 2-nitrobenzothiophene for 3-nitroindoles.Interestingly,4-hydroxyldibenothiophene 8 was directly delivered through a cascade cyclisation/elimination/rearomatisation sequence.The structure could be confimed by1 H NMR,13 C NMR,HPLC,HRMS.Results: We have synthesized 24 hydrocarbazolones derivatives in total.The structures of each compound were confirmed 1H NMR,13 C NMR,HRMS.And the relative configuration of 3a were determined X-ray single crystal diffraction.Hydrocarbazolones derivatives were converted to carbazole compounds with base.We have synthesized 18 dibenothiophene derivatives in total.The structures of each compound were confirmed 1H NMR,13 C NMR,HRMS.Conclusion: We have developed a novel N-heterocyclic carbene-catalysed dearomative [4 + 2] annulation of 3-nitroindoles and β-substituted crotonaldehydes.This organocatalytic protocol was also applied in the oxidative cyclisation of other aromatic systems,such as 2-nitrobenzothiophene,which allowedrapid synthesis of dibenothiophenes.