Osmium(III) and Osmium(V) Complexes Bearing a Macrocyclic Ligand: A Simple and Efficient Catalytic System for cis‐Dihydroxylation of Alkenes with Hydrogen Peroxide

A simple protocol that uses [Os^III(OH)(H₂O)(L ‐N₄Me₂)](PF₆)₂ ( 1 ; L ‐N₄Me₂=N,N′‐dimethyl‐2,11‐diaza[3.3](2,6)pyridinophane) as a catalyst and H₂O₂ as a terminal oxidant for efficient cis‐1,2‐dihydroxylation of alkenes is presented. Unfunctionalized (or aliphatic) alkenes and alkenes/styrenes containing electron‐withdrawing groups are selectively oxidized to the corresponding vicinal diols in good to excellent yields (46–99 %). In the catalytic reactions, the stoichiometry of alkene:H₂O₂ is 1:1, and thus the oxidant efficiency is very high. For the dihydroxylation of cyclohexene, the catalytic amount of 1 can be reduced to 0.01 mol % to achieve a very high turnover number of 5500. The active oxidant is identified as the Os^V(O)(OH) species ( 2 ), which is formed via the hydroperoxide adduct, an Os^III(OOH) species. The active oxidant 2 is successfully isolated and crystallographically characterized.     

Structural Diversity of Copper(I)–N‐Heterocyclic Carbene Complexes; Ligand Tuning Facilitates Isolation of the First Structurally Characterised Copper(I)–NHC Containing a Copper(I)–Alkene Interaction

The preparation of a series of imidazolium salts bearing N‐allyl substituents, and a range of substituents on the second nitrogen atom that have varying electronic and steric properties, is reported. The ligands have been coordinated to a copper(I) centre and the resulting copper(I)–NHC (NHC=N‐heterocyclic carbene) complexes have been thoroughly examined, both in solution and in the solid‐state. The solid‐state structures are highly diverse and exhibit a range of unusual geometries and cuprophilic interactions. The first structurally characterised copper(I)–NHC complex containing a copper(I)–alkene interaction is reported. An N‐pyridyl substituent, which forms a dative bond with the copper(I) centre, stabilises an interaction between the metal centre and the allyl substituent of a neighbouring ligand, to form a 1D coordination polymer. The stabilisation is attributed to the pyridyl substituent increasing the electron density at the copper(I) centre, and thus enhancing the metal(d)‐to‐alkene(π*) back‐bonding. In addition, components other than charge transfer appear to have a role in copper(I)–alkene stabilisation because further increases in the Lewis basicity of the ligand disfavours copper(I)–alkene binding.     

Ruthenium‐Catalyzed Transfer‐Hydrogenative Cyclization of 1,6‐Diynes with Hantzsch 1,4‐Dihydropyridine as a H2 Surrogate

The transfer‐hydrogenative cyclization of 1,6‐diynes with Hantzsch 1,4‐dihydropyridine as a H₂ surrogate was performed in the presence of a cationic ruthenium catalyst of the type [Cp′Ru(MeCN)₃PF₆]. Exocyclic 1,3‐dienes or their 1,4‐hydrogenation products, cycloalkenes, were selectively obtained, depending on the substrate structure and the reaction conditions.     

CuI/glycerol mediated stereoselective synthesis of 1,2-bis-chalcogen alkenes from terminal alkynes: synthesis of new antioxidants

(E)-1,2-Bis-chalcogen alkenes were stereoselectively prepared in good yields by the addition of diorganyl dichalcogenides to terminal alkynes using CuI/Zn/glycerol as a recyclable catalytic system. The antioxidant activity in vitro of four (E)-1,2-bis-chalcogen alkenes synthesized was evaluated and (E)-1,2-bis-(4-methoxyphenylselanyl)styrene 3b presented excellent activity. The catalytic system used in the synthesis was recovered and used directly up to 5 cycles without loss of activity.     

Metal-free oxidative arylphosphination of activated N-substituted-N-arylacrylamide derivatives using K2S2O8

A novel metal-free oxidative arylphosphination of activated N-substituted-N-arylacrylamide derivatives by phosphorylation and C–H functionalization cascade process has been developed. This methodology provides an efficient way to construct a variety of phosphorus-containing oxindole moieties.     

Synthesis of (Z)-N-alkenyl-β-arylselanyl imidazoles via additive-free nucleophilic addition of imidazole to arylselanylalkynes

We present herein our results on the nucleophilic addition of imidazole to a range of arylselanylalkynes by simple heating in DMF without any additives to give (Z)-1-(1-organyl-(2-arylselanyl)vinyl)-1H-imidazoles. The reactions were performed under mild conditions with a range of arylselanylalkynes in good yields and with high regio- and stereoselectivity to give the respective (Z)-arylselanyl alkene as the only isomer.     

rac-BINAP-PdCl2 catalyzed Heck reactions of 3-formylquinolin-2-yl chlorides with methyl acrylate: synthesis of methyl 3-(3-formylquinolin-2-yl) acrylates

rac-BINAP-PdCl₂ catalytic system catalyzed Heck reaction of 3-formylquinolin-2-yl chlorides with methyl acrylate in DMA is described to the synthesis of methyl 3-(3-formyl-quinolin-2-yl)-acrylates, in good to excellent yields. The reaction could be also extended with other activated alkenes to afford Heck products. Fused-benzene ring in heterocyclic and carbocyclic moieties was found to enhance the yields.     

An evidence of contact ion pair in β-(acyloxy)alkyl radical heterolysis during copper(I)-mediated synthesis of trisubstituted alkenes

The first evidence for a unified mechanism of heterolysis in β-(acyloxy)alkyl radical involving contact ion pair (CIP) is presented for both fragmentation and rearrangement of the acyloxy group in the reaction of 1-alkoxy-2,2,2-trichloroethyl acetate with 2 mol equiv each of CuCl and bpy in refluxing DCE under a N₂ atmosphere and availed this reaction for the synthesis of Z-stereoselective trisubstituted alkenes. The stereochemistry of the trisubstituted alkenes was assigned by the uniform pattern of the chemical shift values of some relevant signals in ¹H and ¹³C NMR spectra. This assignment was further supported by the X-ray diffraction spectroscopy of Z-1-chloro-2-(4-nitrobenzyloxy)vinyl acetates.     

Photocatalytic E→Z Contra-Thermodynamic Isomerization of Vinyl Silanes with Lewis Base

Herein, we disclosed the contra-thermodynamic E→Z isomerization of alkenyl silanes, according to the in situ formation of a chromophoric species, in the presence of rac-BINAP as the catalyst. The reaction carried out in DMSO or CH₃CN under irradiation at 405 nm allowed the interconversion of the E-isomers into the Z-congeners in good to excellent yields and outstanding Z/E selectivities, on 18 examples. Finally, the mechanism of this E→Z isomerization was studied to get insight into the reaction mechanism.     

Photo-Induced Dihydroxylation of Alkenes with Diacetyl,Oxygen, and Water

Herein reported is a photo-induced production of vicinal diols from alkenes under mild reaction conditions. The present dihydroxylation method using diacetyl (= butane-2,3-dione), oxygen, and water dispenses with toxic reagents and intractable waste generation.