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.     

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     

Ruthenium(III) chloride-catalyzed efficient protocol for ethyl diazoacetate insertion into the N–H bond of secondary amines

Ruthenium(III) chloride (1 mol%) alone can catalyze the insertion of ethyl diazoacetate into N–H bonds of various structurally and electronically diverse secondary cyclic amines under solvent-free conditions to afford the corresponding glycine esters in good yields under ambient conditions. Reactions with various aliphatic primary and aromatic amines examined, however, were unsuccessful. Correspondence: Dr. Srinivas R. Adapa, Indian Institute of Chemical Technology, Hyderabad 500 007, India.     

Ruthenium(III) chloride-catalyzed efficient protocol for ethyl diazoacetate insertion into the N–H bond of secondary amines

Ruthenium(III) chloride (1 mol%) alone can catalyze the insertion of ethyl diazoacetate into N–H bonds of various structurally and electronically diverse secondary cyclic amines under solvent-free conditions to afford the corresponding glycine esters in good yields under ambient conditions. Reactions with various aliphatic primary and aromatic amines examined, however, were unsuccessful.     

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.     

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.     

Germylenes and stannylenes based on aminobisphenolate ligands: insertion into the C—Br bond

A reaction of previously synthesized germylenes and stannylenes based on aminobisphenols RN{CH₂[(5-R´)(3-But)C₆H₂(2-O—)]}₂M^II, M = Ge, R = CH²(2-Py), R´ = But (1); M = Ge, R = Et, R´ = Me (2); M = Sn, R = CH₂(2-Py), R´ = But (3); M = Sn, R = Et, R´ = Me (4), containing (tetrylenes 1 and 3) or not containing (tetrylenes 2 and 4) a group capable of additional donation, with allyl bromide leads to the products of the insertion of tetrylenes into the C—Br bond: RN{CH₂[(5-R´)(3-Bu^t)C₆H₂(2-O—)]}₂M(Br)All, M = Ge, R = CH₂(2-Py), R´ = But (5); M = Ge, R = Et, R´ = Me (6); M = Sn, R = CH₂(2-Py), R´ = But (7); M = Sn, R = Et, R´ = Me (8). The structures of obtained derivatives were confirmed by NMR spectroscopy and elemental analysis. The structures of compounds 4, 5, and 7 were studied by X-ray crystallography. Stannylene 4 was found to be monomeric in the solid phase: the coordination number of the Sn atom is 3. The insertion products 5 and 7 are characterized by the coordination number 6 for the central atom.     

Aryne insertion into I-I σ-bonds

A new protocol for the efficient synthesis of o-diiodoarenes has been developed. This method allows the synthesis of substituted and polycyclic o-diiodoarenes, which are difficult to obtain by classical methods. This diiodination process involves the formal insertion of arynes into the I-I σ-bond.     

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.     

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.     

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.     

Catalytic generation of zinc carbenes from alkynes: zinc-catalyzed cyclopropanation and sih bond insertion reactions

Think zinc: Synthetically relevant zinc(II) carbenes are catalytically generated from alkynes. This new approach allows zinc-catalyzed cyclopropanation and Si?H bond insertion reactions to generate the corresponding cyclopropylfurans or silane derivatives. The structure of the key carbene intermediate was studied using theoretical methods.     

Insertion of arynes into the carbon–oxygen double bond of amides and its application into the sequential reactions

The reaction of arynes, generated from ortho-(trimethylsilyl)aryl triflates, with the CO bond of formamides gave salicylaldehyde derivatives via the formation of formal [2+2] adducts. The sequential transformation of arynes into ortho-disubstituted arenes, o-aminoalkylphenols or o-hydroxyalkylphenols, was achieved by one-pot procedure using dialkylzincs.     

Catalytic transformation of cellulose and its derived carbohydrates into chemicals involving C–C bond cleavage

The catalytic transformation of cellulose, the major component of abundant and renewable lignocellulosic biomass, into building-block chemicals is a key to establishing sustainable chemical processes. Cellulose is a polymer of glucose and a lot research effort has been devoted to the conversion of cellulose to six-carbon platform compounds such as glucose and glucose derivatives through C–O bond activation. There also exist considerable studies on the catalytic cleavage of C–C bonds in biomass for the production of high-value chemicals, in particular polyols and organic acids such as ethylene glycol and lactic acid. This review article highlights recent advances in the development of new catalytic systems and new strategies for the selective cleavage of C–C bonds in cellulose and its derived carbohydrates under inert, reductive and oxidative atmospheres to produce C1–C5polyols and organic acids. The key factors that influence the catalytic performance will be clarified to provide insights for the design of more efficient catalysts for the transformation of cellulose with precise cleavage of C–C bonds to high-value chemicals. The reaction mechanisms will also be discussed to understand deeply how the selective cleavage of C–C bonds can be achieved in biomass.     

Rhodium catalyzed regioselective arene homologation of aryl urea via double C–H bond activation and migratory insertion of alkyne

A convenient rhodium catalyzed oxidative arene homologation of aniline derivatives with symmetrical or unsymmetrical alkynes using Cu(OAc)_2 as oxidant is described. Urea group is shown to be effective as a directing group for initial ortho C–H activation. Two migratory insertion events of alkyne into Rh–C bond occur successively, both with complete regioselectivity. This method is particularly useful for synthesis of polyarenes with different substituents, which has not been reported with conventional protocol. A mechanism has been proposed to explain the observed data.     

Highly selective intramolecular carbene insertion into primary C-H bond of α-diazoacetamides mediated by a (p-cymene)ruthenium(II) carboxylate complex

Complex [(p-cymene)Ru(η(1)-O(2)CCF(3))(2)(OH(2))] mediated transformation of α-diazoacetamides ArCH(2)N(C(CH(3))(3))C(O)CHN(2) to result in carbene insertion into the primary C-H bond exclusively, with the γ-lactam products being isolated in up to 98% yield. This unexpected reaction is striking in view of the presence of usually more reactive sites such as secondary C-H bonds in the substrates. DFT calculations based on proposed Ru-carbene species provide insight into this unique selectivity.