LongLarf

A copper-catalyzed/silver-promoted desaturation method is described which allows the regioselective conversion of various unactivated N-alkylamides at remote sites to the corresponding N-alkenylamides via N-centred radical mediated 1,5 hydrogen atom transfer, metal-mediated oxidation and deprotonation. The transformation shows good functional group tolerance and can be used for late-stage desaturation of drug derivatives and biologically more relevant compounds.

Abstract

Desaturation of inert aliphatic C−H bonds in alkanes to form the corresponding alkenes is challenging. In this communication, a new and practical strategy for remote site-selective desaturation of amides via radical chemistry is reported. The readily installed N-allylsulfonylamide moiety serves as an N radical precursor. Intramolecular 1,5-hydrogen atom transfer from an inert C−H bond to the N-radical generates a translocated C-radical which is subsequently oxidized and deprotonated to give the corresponding alkene. The commercially available methanesulfonyl chloride is used as reagent and a Cu/Ag-couple as oxidant. The remote desaturation is realized on different types of unactivated sp³-C−H bonds. The potential synthetic utility of this method is further demonstrated by the dehydrogenation of natural product derivatives and drugs.

Abstract

A synthetically useful Z-selective cascade formal thiyl radical addition, 1,3-double bond isomerization, oxygen trapping reaction, can be promoted by Eosin B under visible light, leading to the construction of 2-aryl- and alkylthio enone derivatives in good yields. An accurate study on the reactivity of different thiols and the screening of the reaction conditions, allowed us to extend this reaction to a large number of substrates, showing a good functional groups tolerance while highlighting the limitations of this procedure. Background experiments and mechanistic studies were also. performed to rationalize this cascade process. The usefulness of this methodology was finally demonstrated via the transformation of a series of α-sulfanyl-enone adducts through selected oxidation reactions, stereoselective synthesis of cyclopropyl ketones, indanones, and pyrazole compounds.

Abstract

Lignin valorization allows the generation of a number of value-added products such as cis,cis-muconic acid (ccMA), which is widely used for the synthesis of chemicals for the production of biodegradable plastic materials. In the present work, we reported the first multi-enzymatic, one-pot bioconversion process of vanillin into ccMA. In details, we used four sequential reactions catalyzed by xanthine oxidase, O-demethylase LigM (and the tetrahydrofolate-regeneration enzyme methyl transferase MetE), decarboxylase AroY (based on the use of E. coli transformed cells) and catechol 1,2-dioxygenase CatA. The optimized lab-scale procedure allowed to reach, for the first time, the conversion of 5 mM vanillin into ccMA in ∼30 h with a 90% yield: this achievement represents an improvement in terms of yields and time when compared to the use of a whole-cell system. This multi-enzymatic system represents a sustainable alternative for the production of a high value added product from a renewable resource.

Abstract

A phosphine-mediated reaction for the construction of spirocyclopenta[c]chromene-indolinones is reported via a Rauhut-Currier (RC)-type/acyl transfer/Wittig sequence. This methodology attributes the chemoselective phosphine addition to the alkynoate which generates the phosphorus zwitterion via RC-type reaction, and that further undergoes O-acylation to form the seven-membered betaine intermediate with acyl chloride in the presence of base. Extensive investigations reveal that the exceptional δ-acylation occurs through the C−O bond cleavage upon the seven-membered betaine, and the subsequent Wittig reaction preferentially result in the aforementioned spiro compounds. Furthermore, our protocol could also be applicable to different alkynoates to provide a series of spirocyclopenta[c]chromenones bearing privileged skeletons.

Publication date: 22 October 2021

Source: Tetrahedron, Volume 99

Author(s): Fritz Schömberg, Milica Perić, Maximilian Meyer, Ivan Vilotijević

Publication date: 5 November 2021

Source: Tetrahedron, Volume 100

Author(s): Jie Feng, Ding Du

Publication date: 22 October 2021

Source: Tetrahedron, Volume 99

Author(s): Jagannath Rana, Satabdee Tanaya Sahoo, Prosenjit Daw

We describe the step-wise synthesis of the novel cyapho-cyanamide ion, [N(CN)(CP)]⁻, obtained by the reaction of sodium phosphanide, Na(PH₂), with dimethyl N-cyanocarbonimidate, (MeO)₂C=N(CN). Preliminary reactions of the ion with electrophiles reveal the cyclisation reactions are available on functionalisation.

Abstract

We describe a facile synthesis of the cyapho-cyanamide salt [Na(18-crown-6)][N(CN)(CP)] from reaction of [Na(18-crown-6)][PH₂] (18-crown-6=1,4,7,10,13,16-hexaoxacyclooctadecane) with dimethyl N-cyanocarbonimidate, (MeO)₂C=N(CN). The reaction proceeds with elimination of two equivalents of methanol. Careful tuning of the reaction conditions allowed for the isolation and characterization of the N-cyano(carboximidate)phosphide intermediate [HP{C(OMe)N(CN)}]⁻. Due to the adverse effects of methanol in these reaction mixtures, a bulk scale synthesis of [Na(18-crown-6)][N(CN)(CP)] could be achieved by addition of a base (LiHMDS) to neutralize the resulting alcohol. Further reactivity studies of this anion reveal that functionalization at the phosphorus atom is viable to yield a new family of cyanide-functionalised phosphorus heterocycles.