Tetrahedron Letters最新文献

A method for transition-metal-free sulfenylation of pyrrolo[1,2-a]quinoxalines was developed. Selective functionalization of C1H bonds was achieved via an electrophilic substitution with thiodiazonium adduct presumably derived from combination of sulfonyl hydrazides and molecular iodine. The conditions were well tolerated with a wide range of functionalities as well as heterocycles. Our method would offer a rare example for direct sulfenylation of C1H bonds in pyrrolo[1,2-a]quinoxalines in the absence of transition metals or strong oxidants.

A practical and highly efficient method for the regioselective synthesis of isoquinolines was developed via cobalt-catalyzed C(sp²)−H activation and subsequent intramolecular tandem annulations between benzimidates and sulfoxonium ylides. Key to the success of this transformation was the use of an inexpensive and bench-stable Cp*Co(III)-catalyst. Various functionalized isoquinolines were prepared successfully under base-free and oxidant-free conditions. This protocol features simple operation, broad substrate scope, and good functional group tolerance. Moreover, the reaction is scalable and tolerant of ambient air and moisture.

A new [4 + 3] annulation between isatin N,N′–cyclic azomethine 1,3-dipole and nitrosoalkenes in situ generated from α-haloketone oximes has been disclosed. This new protocol is tolerable for a series of substrates and a novel series of seven-membered spiro oxindoles containing oxygen and nitrogen atoms were obtained in moderate to good yields (up to 83 %) under mild conditions.

The first total synthesis of (+)-epicolidine C has been accomplished via a late-stage HfCl₄-mediated epoxide opening from (+)-PF1052. The 6/6/6/5 tetracyclic core of spylidone has also been constructed from (+)-AB4015-B via late-stage iodine(I)- or manganese(III)-mediated oxidative cyclization reactions, whose absolute stereostructure was unambiguously confirmed by X-ray crystallographic analysis.

A general organocatalytic method has been developed for the asymmetric synthesis of α-hydrazino-γ-fluoro alcohols, a precursor to syn/anti-1,3-fluoro amines. The strategy employs α-fluorination catalyzed by proline-derived catalyst, (S)-α,α-bis[3,5-bis(trifluoromethyl)phenyl]-2-pyrrolidinemethanol trimethylsilyl ether followed by Horner−Wadsworth−Emmons (HWE) olefination of aldehydes, and proline-catalyzed α-amination as the key steps. The title compounds showed excellent diastereoselectivity (up to 99:1) and enantioselectivity (up to 99 %).

A novel electrophilic ferrocenylating reagent, thianthrene-based S-ferrocenyl sulfonium salt, has been be synthesized in one pot from ferrocenyl lithium. This bench-stable ferrocenylating reagent shows excellent thermos-stability and reactivity, and has been demonstrated to allow access to complex ferrocene architectures from various terminal alkenes or alkynes.

During the last years diverse Pillar[n]arenes have been intensively used as molecular systems for recognition and synthons for self-assembly, toward the construction of highly selective supramolecular materials or functional devices. They present an electron-rich cavity, as well as reactive rims that can be decorated with specific functional groups, resulting in the formation of tubular pillar shape architectures. For this reasons pillar[n]arenes are excellent candidates for the construction of artificial water, ionic, proton, or molecular channels through bilayer and polymeric membranes used for selective membrane separations. This review integrate the most recent examples of pillar[n]arenes synthetic systems used to elaborate selective channels or nanodevices for selective water translocation, ion or proton rectification useful for important application in environmental sciences as water purification or medicine.

This paper reports the total synthesis of antibacterial cyclic hexapeptides nicrophorusamides A (1) and B (2), isolated from the actinomycete strain UTG9 belonging to the genus Microbacterium. The synthesis involved solid-phase peptide elongation and solution-phase macrolactamization, followed by the removal of the protecting groups. Synthetic 1 and 2 demonstrated inhibitory effects on the growth of S. aureus, with minimum inhibitory concentration (MIC) values of 8 μg/mL and 16 μg/mL, respectively, determined using the broth microdilution method.

Herein we report improved shorter and practical synthesis of known enone-ester intermediate 12 as a gateway to anticancer Δ¹²-Prostaglandin J₃. Several one-pot methods were developed to synthesize azide 5 directly from enal 1, ene-carbamate 7 directly from lactone-acid 4 and enone-acid 11 directly from azide 5. The step count (from 12 to 8 steps) improvements achieved makes this formal synthesis of Δ¹²-Prostaglandin J₃ one of the shortest.

An alternative strategy for the synthesis of β-aminoketones have been achieved through silver(I)-catalyzed and DBU-promoted isomerization/addition of propargyl alcohols to amines. The mechanism likely involves an isomerization and sequential addition combined with the alkenyl radical process. This protocol features broad substrate scope, superior atom economy, operational simplicity, and good to excellent yields, and provides a new method for the synthesis of drug Proroxan on gram-scale, presenting a practical application for the construction of β-aminoketones.