RESUMEN
A dual InBr3-EtAlCl2 Lewis acidic system was found to be optimal for promoting the diastereoselective (3 + 2)-cycloaddition of donor-acceptor cyclopropanes with in situ-generated ketenes to form cyclopentanones. The desired products were formed in good to excellent yields (70-93% for 16 examples) and with good to excellent diastereoselectivity and enantiospecificity.
RESUMEN
A versatile asymmetric synthesis of bicyclic pyrazolidinones through alkaloid-catalyzed formal [3+2]- and [3+2+2]-cycloadditions of ketenes with azomethine imines is described. The methodology was found to be tolerant of ketene and a variety of monosubstituted ketenes (R=alkyl, OAc). The products were formed in good to excellent yields (71-99 % for 24 examples, 39 examples in all), with good to excellent diastereoselectivity in many cases (dr 3 : 1 to 27 : 1 for 22 examples), and with excellent enantioselectivity for most examples (≥93 % ee for 34 products). In the case of most disubstituted ketenes, the reaction proceeded through a [3+2+2]-cycloaddition to form structurally interesting bicyclic pyrazolo-oxadiazepinediones with moderate diastereoselectivity (dr up to 3.7 : 1) and as racemic mixtures (3 examples). The method represents the first unambiguous example of an enantioselective reaction between ketenes and a 1,3-dipole.
Asunto(s)
Alcaloides , Iminas , Compuestos Azo , Catálisis , Reacción de Cicloadición , Estereoisomerismo , TiosemicarbazonasRESUMEN
This study confirms the hypothesis that bambusurils (BUs) with equatorial sulfur atoms cannot assume an anion-binding jigger conformation due to strong intramolecular van der Waals attractive interactions. NMR, X-ray crystallography, and computation with newly synthesized eq-semithio-BU[4] and ax-semiaza-eq-semithio-BU[4]s indicate that they all assume compact conformations. Intramolecular distances and a torsional angle serve as reliable indicators of the conformation of any BU. Chemoselective alkylation at the peripheral (equatorial) thiourea functions provides a convenient entry to novel hetero-BUs.
RESUMEN
A visible light mediated, metal-free process for the thiocyanation of imidazoheterocycles has been developed using eosin Y as a photoredox catalyst under ambient air at room temperature. A library of 3-(thiocyanato)imidazo[1,2-a]pyridines with broad functionalities have been synthesized in high yields. This methodology is also applicable for the selenocyanation of imidazo[1,2-a]pyridine.
RESUMEN
Iodine-catalyzed regioselective sulfenylation of imidazo[1,2-a]pyridines via C(sp(2))-H bond functionalization has been achieved using sulfonyl hydrazides as a thiol surrogate. A library of 3-sulfanylimidazopyridines with broad functionalities was synthesized under metal and oxidant-free practical reaction conditions. This methodology is also applicable for the regioselective sulfenylation of imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole.
Asunto(s)
Hidrazinas/química , Yodo/química , Piridinas/química , Compuestos de Sulfhidrilo/química , Compuestos de Sulfhidrilo/síntesis química , Catálisis , Estructura Molecular , EstereoisomerismoRESUMEN
The FeCl3/ZnI2-catalyzed aerobic oxidative cyclization between 2-aminobenzothiazole and ketone/chalcone for the synthesis of benzo[d]imidazo[2,1-b]thiazole is described. A variety of fused benzoimidazothiazole derivatives are obtained by this protocol.
Asunto(s)
Benzotiazoles/química , Cloruros/química , Compuestos Férricos/química , Yoduros/química , Cetonas/química , Tiazoles/síntesis química , Compuestos de Zinc/química , Catálisis , Ciclización , Estructura Molecular , Oxidación-Reducción , Tiazoles/químicaRESUMEN
An unprecedented formation of benzothiazine during copper(I)-catalyzed oxidative coupling of 2-aminobenzothiazole and terminal alkyne in air has been observed. This unique transformation possibly occurs through the ring opening of 2-aminobenzothiazole and subsequent oxidative coupling with alkyne followed by intramolecular cyclization. A variety of substituted benzo[b][1,4]thiazine-4-carbonitriles are obtained by this protocol.
RESUMEN
We report in this work an environmentally benign zinc mediated synthesis of aryl and benzyl phosphorochalcogenoates in ethanol within a short reaction time. In vitro antimicrobial study along with statistical analysis and seed germination assay were performed. These chalcogenophosphates possess strong antimicrobial activity against the reference strains. The antibacterial activity was determined against four standard strains (Bacilus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa). The antifungal activity was evaluated against one fungal strain Candida albicans.