Parameterization of Acyclic Diaminocarbene Ligands Applied to a Gold(I)-Catalyzed Enantioselective Tandem Rearrangement/Cyclization
A convergent and regioselective synthesis of silicon-bridged 4-arylpyridines has been developed through a rhodium-catalyzed [2+2+2] cycloaddition of silicon-containing diynes with nitriles. The absorption and emission properties of these compounds have been examined and could be tuned by varying the substituent on the benzene ring, as well as through the protonation or alkylation of the nitrogen atom on the pyridine ring. A catalytic asymmetric synthesis of silicon-centered axially chiral spirocyclic derivatives has also been achieved with high enantioselectivity by using a newly modified MeO-MOP (MeO-MOP=2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthyl) derivative as the chiral ligand. These spirocyclic compounds were found to be CPL-active (CPL=circularly polarized luminescence), representing the first CPL-active compounds based on the chirality at silicon.
A convergent and regioselective synthesis of silicon-bridged 4-arylpyridines has been developed through a rhodium-catalyzed [2+2+2] cycloaddition of silicon-containing diynes with nitriles. The catalytic asymmetric synthesis of silicon-centered axially chiral spirocyclic compounds and their optical properties have also been investigated.
N-Iodosuccinimide-Promoted Rapid Access to Indeno[1,2-c]pyrroles via [3+2] Annulation of Enamine-alkynes
We have developed a metal-free, N-iodosuccinimide (NIS)-promoted, cascade strategy for the efficient synthesis of biologically important indeno[1,2-c]pyrroles via a [3+2] annulation process of enamine-alkynes. This methodology had shown a very broad scope for diversely functionalized enamines and alkynes. We have also developed a one-pot, multicomponent strategy for the direct synthesis of indeno-pyrroles from diynones via enamine-alkynes. Control experiments supported the involvement of NIS as an electrophilic activator via an ionic mechanism rather than a radical pathway.
Synthetic Study of Rubriflordilactone B: Highly Stereoselective Construction of the C-5-epi ABCDE Ring System
Rhodium(I)-Catalyzed [2+2+2] Cycloaddition between Allene, Alkyne, and Imine via a Strained Azarhodacycle Intermediate
The rhodium(I)-catalyzed intramolecular [2+2+2] cycloaddition between allenes, alkynes, and imines has been developed. This cyclization proceeds via a strained azarhodacycle, giving a 5,7-fused cyclic amide or a tricyclic product containing an 8-azabicyclo[3.2.1]octane skeleton in high yield.
A new method for the preparation of optically active α-methylidene-δ-lactones is presented. The developed strategy utilizes an intramolecular Rauhut–Currier reaction for a facile construction of the α-methylidene-δ-lactone framework. The reaction is catalyzed by a chiral phosphine and employs the principles of nucleophilic catalysis. It benefits from operational simplicity and uses readily available starting materials.
© Georg Thieme Verlag Stuttgart · New York
Cyano-Schmittel Cyclization through Base-Induced Propargyl-Allenyl Isomerization: Highly Modular Synthesis of Pyridine-Fused Aromatic Derivatives
The cyano-Schmittel cyclization of in situ-generated cyano-allenes has been carried out. The DFT calculation results suggest that the diradical pathway plays a major role in this cyclization. The reactions can be conveniently performed in a one-pot manner through cascade Sonogashira coupling of terminal cyano-ynes with organic halides, followed by base-promoted propargyl-allenyl isomerization/cyclization, leading to an efficient access to pyridine-fused polycyclic architectures. In particular, a large variety of aryl or heteroaryl rings such as furans, thiophenes and pyridines can be incorporated into the follow-up cyano-Diels–Alder reactions, highlighting the great synthetic utility of this chemistry.
I cyano what you did last summer: The cyano-Schmittel cyclization of in situ-generated cyano-allenes is described. The reactions can be conveniently performed in a one-pot manner through cascade Sonogashira coupling of terminal cyano-ynes with organic halides, followed by base-promoted propargyl-allenyl isomerization/cyclization, leading to an efficient access to pyridine-fused polycyclic architectures.
An Eco-Friendly Route to N-Arylindoles by Iron-Catalyzed [2+2+2] Cycloaddition of Diynes with (Indol-1-yl)alkynes
A new pathway to the synthesis of N-arylindoles has been developed that proceeds through an iron-catalyzed [2+2+2] cycloaddition reaction between diynes and indole-N-alkynes. The reaction is carried out in ethanol and employs a catalyst system that consists of iron(II) chloride tetrahydrate as the metal source, 2-[(2,6-diisopropylphenyl)iminomethyl]pyridine (dipimp) as the ligand, and zinc as the reducing agent. The method provides efficient access to 3-carbonyl/ester-substituted (indol-1-yl)arenes in good to excellent yields under green reaction conditions, and these products are structurally similar to other N-arylindole derivatives with potential medicinal value.
A new method for the synthesis of N-arylindoles by using a [2+2+2] cycloaddition reaction between diynes and indole-N-alkynes has been established. This protocol employs FeCl2·4H2O/2-[(2,6-diisopropylphenyl)iminomethyl]pyridine (dipimp)/Zn as the catalyst system and ethanol as the solvent and provides easy access to indole-N-substituted fused arenes under green reaction conditions.
Synthesis of phthalides from bis-propargyl ethers: use of Garratt–Braverman cyclization to construct the phthalans and IBX as a new reagent for subsequent oxidation
Source:Tetrahedron Letters, Volume 56, Issue 44
Author(s): Arpita Panja, Eshani Das, Manasi Maji, Amit Basak
An efficient route to phthalides is described starting from easily available bis-propargyl ethers. The method involves Garratt–Braverman cyclization of the ethers to phthalans which are then efficiently oxidized to the phthalides by iodoxy benzoic acid (IBX) which has been shown to be a superior reagent in terms of yield and reagent stoichiometry for such a transformation in comparison with more commonly used KMnO4/CuSO4 reagent.