Metallophthalocyanine-catalyzed cyclopropanation

Metallophthalocyanine-catalyzed carbenoid reactions have had little attention to date. Recently these metal complexes have been found to catalyze cyclopropanation reactions. We have investigated these metallophthalocyanines in reactions to catalyze cyclopropanation from donor–acceptor carbenoids. The yields and diastereoselectivity of these reactions are influenced by the nature of the styrene as well as the aryldiazoacetate and catalyst. The products have been synthesized in short reaction times (1 h), with good yields (up to 84%), and high diastereoselectivity (up to 20:1 ratio cis/trans products).     

Efficient one-pot synthesis of biologically interesting diverse furo[2,3-b]pyran-6-ones by rhodium(II)-catalyzed cascade reactions of diazo compound with ethynyl compounds

Rhodium(II)-catalyzed reactions of diazo compound and a variety of ethynyl compounds were carried out. These reactions provide a rapid route for preparing a variety of furo[2,3-b]pyran-6-one derivatives in one-pot via cascade reactions of metal carbenoid reaction/ketene formation/[2+2]cycloaddition/ring expansion.     

Phosha-Meerwein Reaction of Diazo Esters

Abstract

Diazo esters (la,b) react with trialkyl phosphates (2a–c) in the presence of BF₃.OEt₂ to give the corresponding phosphates (3a–e) in 42–58 % yields. The competed intra/intermolecular protonation in the reaction of la with dimethyl hydrogen phosphite leads to phosphonate. 4,and phosphite 5.     

Multicomponent reactions involving p-benzoquinones, diazo esters, titanium(IV) isopropoxide and alcohol in the presence of rhodium(II) acetate as catalyst

A Rh₂(OAc)₄ catalyst derived oxonium ylide intermediate underwent nucleophilic addition with the CC or CO bond of p-benzoquinones. The syntheses of 2-substituted hydroquinones and 1-hydroxy-4-oxocyclohexa-2,5-dienyls have been demonstrated.     

Unprecedented cyclization of α-diazo hydrazones upon N-H functionalization: A Et3N base promoted one-step synthetic approach for the synthesis of N-amino-1,2,3-triazole derivatives from α-diazo hydrazone

In this communication, for the first time, we are reporting α-diazo hydrazone synthesis from hydrazones derived from β-keto esters and 2,4-dinitro phenyl hydrazine via diazo transfer reaction. We also report an unexpected cyclization of the α-diazo hydrazones upon N-H functionalization to give highly functionalized N-amino-1,2,3-triazole derivatives under metal-free condition. This one-step synthetic protocol can serve as a general tool to access nitrogen rich 5- and 6-membered heterocycles in excellent yields.     

DBU-catalyzed condensation of acyldiazomethanes to aldehydes in water and a new approach to ethyl β-hydroxy α-arylacrylates

DBU-catalyzed condensation of ethyl diazoacetate (EDA) with aldehydes in pure water afforded corresponding β-hydroxy α-diazo carbonyl compounds. The β-hydroxy group of the products was further converted into β-siloxy group. The Rh(II)-catalyzed reaction of the β-aryl β-siloxy α-diazo carbonyl compounds gave 1,2-aryl shift products predominantly. The three-step transformation constitutes an efficient synthesis of ethyl β-hydroxy α-arylacrylates.     

New reaction of enamines with aryldiazoacetates catalyzed by transition metal complexes

The reaction of aryldiazoacetates with enamines catalyzed by copper and rhodium complexes provided γ-keto esters in good yields. A full investigation of the effects of solvents, catalysts, enamines and aryldiazoacetates on the reaction was carried out. Careful analysis of the crude reaction mixture revealed a substituted enamine as the primary product, which was hydrolyzed over silica gel to give a γ-keto ester as the final product. A reaction mechanism involving nucleophilic addition of an enamine to a metal carbene and subsequent hydrogen transfer was proposed. Chiral dirhodium and copper catalysts were examined and found to provide γ-keto esters with no enantioselectivity. The result could be rationalized based on the proposed reaction mechanism. Attempts to trap the enamine intermediate with several electrophilic reagents were not successful.     

Synthesis and reactions of a monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide

A 3-monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide, was prepared for the first time, by the reaction of (9-triptycyl)diazomethane and S₈O. The dithiirane 1-oxide was obtained as cis- and trans-isomers, and the structure of the trans-isomer was verified by X-ray crystallography. The cis-isomer isomerized gradually to the trans-isomer in solution. The divalent sulfur atom of the cis- and trans-dithiirane 1-oxides were removed on treatment with triphenylphosphine to give the corresponding Z- and E-sulfines, respectively. The reaction of the trans-dithiirane 1-oxide with (Ph₃P)₂Pt(C₂H₄) provided the (sulfenato-thiolato)Pt^II complex, and that with Lawesson's reagent yielded the 1,3,4,2-trithiaphospholane and 1,2,4,5,3-tetrathiaphosphorinane derivatives.     

Kinetics and Mechanism of the Reaction between an Arenediazonium Ion and Methyl Gallate (=Methyl 3,4,5‐Trihydroxybenzoate) in Aqueous Solution: Evidence for Diazo Ether Formation through an O‐Coupling Reaction

We have investigated the kinetics and mechanism of the reaction between 3‐methylbenzenediazonium ions (3MBD) and methyl gallate (=methyl 3,4,5‐trihydroxybenzoate; MG), in aqueous buffer solution by employing spectrophotometric (UV/VIS) and electrochemical (linear‐sweep voltammetry, LSV) techniques and computational methods. Because the absorption band of MG overlaps that of 3MBD, the reaction was monitored spectrophotometrically by measuring the changes in absorbance with time due to product formation, and biphasic kinetic profiles, indicative of accumulation of an intermediate in the course of the reaction, were obtained. The formation of an intermediate was confirmed by LSV. The observed rate constants k_obs for 3MBD disappearance were obtained by fitting the decrease in the peak current of the first reduction peak of 3MBD with time to the integrated first‐order equation. The variation of k_obs with [MG] was determined at different pH values and follows a saturation kinetic pattern. Alternatively, at a fixed [MG], k_obs values show an inverse dependence on [H⁺], suggesting that the reactive species is the anion and not the neutral form of MG. To discern which of the three OH groups of MG is the first one undergoing deprotonation, the geometries of the resulting anions were optimized by using B3LYP hybrid density functional theory (DFT) and a 6‐31G(++d,p) basis set. The deprotonation energies suggest that the OH group at the 4‐position is first deprotonated. The kinetic results can be accommodated, therefore, by assuming two competitive mechanisms, the spontaneous D_N+A_N decomposition involving 3MBD, and a mechanism involving an electrophilic attack at the O‐atom at C(4) in a pre‐equilibrium step, leading to the formation of a transient diazo ether of the type Ar? N?N? O? R which further decomposes. All attempts to isolate and characterize the diazo ether failed.     

Desymmetrization of meso [3.2.1]oxabicyclic systems using metal-catalysed asymmetric intramolecular C-H insertion

Diazoketone derivatives of meso 8-oxabicyclo[3.2.1]octen-3-ones were desymmetrized by an intramolecular C-H insertion mediated by chiral copper and dirhodium catalysts to generate oxatricyclic systems with up to 5 contiguous stereogenic centres and 50% ee.