Brønsted acid catalyzed formal insertion of isocyanides into a C-O bond of acetals

The Br?nsted acid catalyzed formal insertion of an isocyanide into a C-O bond of an acetal is described. A diverse array of acyclic and cyclic acetals can be applied to the catalytic insertion to form alpha-alkoxy imidates. Functional groups, such as nitro, cyano, halogen, ester, and alkoxy groups, are tolerant to the reaction conditions employed. The course of the reaction is highly dependent on the structure of the isocyanide. The use of an electron-deficient aryl isocyanide, such as 2c and 2d, is required to selectively obtain the monoinsertion product. When aryl isocyanides containing alkyl substituents, such as 2a and 2b, are employed, two molecules of the isocyanide are incorporated, and the double-insertion product is obtained. The reaction of tert-octyl isocyanide also induces a double incorporation, but the subsequent acid-mediated fragmentation leads to the 2-alkoxy imidoyl cyanide. The monoinsertion products, alpha-alkoxy imidates, can readily be hydrolyzed to alpha-alkoxy esters, realizing the formal carbonylation of an acetal.     

The insertion of terminal phosphinidene complexes into the bh bond of amine and phosphine boranes

Push-pull complexation: Transient terminal phosphinidene complexes [RP?W(CO)(5) ] insert at 110?°C into the B?H bonds of L?BH(3) (L = Et(3) N, Ph(3) P; see scheme). The reaction is probably driven by an interaction between the nucleophilic boron and the electrophilic phosphorus.     

A formal insertion of dichlorocarbene into a CArS bond

Reaction of phase transfer generated dichlorocarbene with 9-thiomethylphenanthrene (4) leads to 6 rather than the expected addition product 5. 6 is formally derived from a carbene insertion into the C,S bond. ¹³C-labelling shows that the CH₃ group of 4 is lost during the reaction.     

Amidinate bromogermylene resulting from carbodiimide insertion into Ar–GeBr bond

The reaction of diaryldibromodigermene Tbb(Be)Ge = Ge(Br)Tbb (Tbb = 4-Bu^t-2,6-[CH(SiMe₃)₂]₂C₆H₂) with N,N'-diisopropyl-carbodiimide afforded the corresponding amidinato-supported bromogermylene via the insertion of the C=N moiety into the Ge–C(Tbb) sss-bond. The formation mechanism of the amidinato-supported bromogermylene was revealed by DFT calculations. This type of insertion reaction toward a metal–carbon bond can be interpreted in analogy to the reactivity of transition-metal complexes.     

Dibromomethyl- and bromomethyl- or bromo-substituted benzenes and naphthalenes: C—Br…Br interactions

The structures of six benzene and three naphthalene derivatives involving bromo, bromomethyl and dibromomethyl substituents, namely, 1,3-dibromo-5-(dibromomethyl)benzene, C₇H₄Br₄, 1,4-dibromo-2,5-bis(bromomethyl)benzene, C₈H₄Br₆, 1,4-dibromo-2-(dibromomethyl)benzene, C₇H₄Br₄, 1,2-bis(dibromomethyl)benzene, C₈H₆Br₄, 1-(bromomethyl)-2-(dibromomethyl)benzene, C₈H₇Br₃, 2-(bromomethyl)-3-(dibromomethyl)naphthalene, C₁₂H₉Br₃, 2,3-bis(dibromomethyl)naphthalene, C₁₂H₈Br₄, 1-(bromomethyl)-2-(dibromomethyl)naphthalene, C₁₂H₉Br₃, and 1,3-bis(dibromomethyl)benzene, C₈H₆Br₄, are presented. The packing patterns of these compounds are dominated by Br…Br contacts and C—H…Br hydrogen bonds. The Br…Br contacts, shorter than twice the van der Waals radius of bromine (3.7 Å), seem to play a crucial role in the crystal packing of all these compounds. The occurrence of Type I and Type II interactions is also discussed briefly, considering the effective atomic radius of bromine, as is their impact on the packing of molecules in the individual structures.     

Ab initio MO study of ethylene insertion into the Sm–C bond of H2SiCp2SmCH3

Ethylene insertion into the Sm–C bond of H₂SiCp₂SmCH₃, a model reaction of an olefin polymerization propagation step, has been studied by ab initio molecular orbital methods. The small electronegativity of the Sm atom makes the Sm–C bond ionic, the methyl group being negatively charged by −0.75. The reaction passes through a loose ethylene complex with a binding energy of 15 kcal/mol and then a tight four-centered transition state with an agostic interaction between the Sm atom and one of the methyl CH bonds. A small activation energy of 14 kcal/mol is required to pass through this transition state, indicating that this is an easy reaction. Compared with the reactions with group 4 cationic silylene-bridged metallocenes the activation energy is higher and the reaction is less exothermic. The origin of these differences is discussed. The results of molecular mechanics calculations on regio- and stereoselectivities in the insertion reaction of propylene are also reported. Received: 13 July 1998 / Accepted: 28 August 1998 / Published online: 2 November 1998     

Regioselective insertion of carborynes into ethereal C-H bond: facile synthesis of α-carboranylated ethers

Carborynes can exist in two resonance forms, bonding form vs biradical form. The biradical form can be readily generated via the elimination of LiI from 1-iodo-n-lithio-1,n-C(2)B(10)H(10) (n = 2, 7) under UV irradiation. They can undergo α-C-H bond insertion with aliphatic ethers, affording α-carboranylated ethers in excellent regioselectivity at room temperature. This serves as a new methodology for the generation of a series of functionalized carboranes bearing alkoxy units.     

Review: Single-molecule magnets based on pyridine alcohol ligands

Single-molecule magnets (SMMs) have attracted attention due to their potential applications in quantum computation and information storage, and many SMMs have been reported in the past two decades. In this review, we summarize the structures and the magnetic exchange interactions of pyridine alcohol-based SMMs to give a possible relationship between structure and magnetic property, providing information to generate new molecule-based magnetic materials. According to the correlated metal centers, these SMMs are separated into three segments to discuss.     

N-Perhalofluoroalkylation of secondary amines by the reactions of the amines and amides with perhalofluoroalkanes. Halophilic attack on nitrogen nucleophile on CBr bond.

Secondary amines and amides react spontaneously with perhalofluoroalkanes CF₂BrCFBrX(X = F, Cl, CF₃) to afford N-perhalofluoroalkylated tertiary amines in fair to good yields. Evidence for an anionic chain process initiated by the bromophilic attack of nitrogen nucleophiles on CBr bonds is given.     

Reactivity of zirconocene and hafnocene dihydrides towards elemental selenium and sulfur. Strong evidence for insertion of a chalcogen unit into the metal—hydrogen bond

Dimeric metallocene dihydrides [(η⁵-t-BuC₅H₄)₂MH(μ-H)]₂ (1; M = Zr, Hf) react with elemental chalcogens to give the four-membered metallacycles [(η⁵-t-BuC₅H₄)₂M(μ-E)]₂ (2, E = Se; 3, E = S). In the case of sulfur, the reaction also gives (η⁵-t-BuC₅H₄)₂MS₅ (4). Both 3 and 4 are shown to come from subsequent reactions of the primary insertion product (η⁵-t-BuC₅H₄)₂M(SH)₂.     

Pincer ligands based on α-amino acids: III. New ligands based on 4-substituted phenols and their copper complexes. Enantioselective recognition of tyrosine

Reactions of L-methionine, L-serine, and L-valine with 5-substituted-2-hydroxybenzene-1,3-dicarbaldehydes gave a series of chiral Schiff base pincer ligands which were reduced to the corresponding diamines. The new Schiff base ligands reacted with copper(II) chloride to form dinuclear copper complexes which were found to be capable of recognizing tyrosine enantiomers in aqueous solution. The structure of the complexes was determined on the basis of their spectral parameters.     

Rhodium-catalyzed CC bond formation by ring-opening of alkylidenecyclopropanes and insertion of 3-butenoic acid

Diphenylmethylenecyclopropane reacts with 3-butenoic acid in the presence of RhCl(PPh₃)₃ to give products resulting from insertion of one or two molecules of butenoic acid. Insertion of the first molecule of butenoic acid is not regioselective, whereas insertion of the second is highly regioselective.     

Electronic effects of aryl-substituted bis(oxazoline) ligands on the outcome of asymmetric copper-catalysed C–H insertion and aromatic addition reactions

The effect of the modification of bis(oxazoline) ligands on the outcome of copper-catalysed C–H insertion and aromatic addition reactions is described. In general, these reactions display minimum sensitivity in terms of enantiocontrol to variation of the electronic properties of the aryl moiety of the ligand however, some influence is observed for C–H insertions employing naphthyl-substituted bis(oxazolines) and for aromatic addition reactions of biphenyl diazo ketone substrates. The synthesis of the modified bis(oxazolines), which include four novel structures, is also described.     

Synthesis and structure of the first dinuclear gold complex with the Au—Au bond containing no bridging ligands

Russian Chemical Bulletin -     

Highly selective insertion of arynes into a C(sp)-O(sp3) σ bond

Arynes react with ethoxyacetylene to afford 2-ethoxyethynylaryl derivatives through a highly chemo- and regioselective formal insertion of the aryne into the C(sp)-O(sp(3)) bond of the alkyne. Computational studies suggest that the reaction does not proceed through a mechanism initiated by the nucleophilic addition of the oxygen atom to the aryne as previously proposed but by the addition of the triple bond of the alkyne to the aryne.     

Iodine and Brønsted acid catalyzed C–C bond cleavage of 1,3-diketones for the acylation of amines

Abstract

A metal-free N-acylation method of anilines with 1,3-diketones has been developed, by using iodine and p-toluene sulfonic acid as the co-catalysts. The reaction can proceed in 1,4-dioxane at elevated temperature to produce the corresponding amides with 48–89% yields. Further, the gram-scale experiment was carried out under the standard conditions and the possible mechanism was proposed.     

Iridium pentahydride complex catalyzed formation of CC bond by CH bond activation followed by olefin insertion

The formation of carbon-carbon bond was found to occur by first carbon-hydrogen bond activation followed by olefin insertion under the catalysis of an iridium pentahydride complex.     

Facile synthesis of 2-nitromethyl aromatic ketones by insertion of benzynes into the C-C bond of α-nitroketones

A facile method to synthesize 2-nitromethyl aromatic ketones was developed. In the method, benzyne was generated in situ for the insertion to α-Nitroketones in one pot to achieve 2-nitromethyl aromatic ketones under mild conditions. Aromatic and aliphatic α-nitroketones were applied in the reaction, and the results show that aliphatic α-nitroketones gave excellent yields (up to 96%), while aromatic α-nitroketones gave moderate yields. The synthesized 2-nitromethyl aromatic ketones could be potential substrates to synthesize isoindoles.