Unprecedented double C-C bond cleavage of a cyclopentadienyl ligand

Double C-C bond cleavage of a cyclopentadienyl ligand proceeded to titanacyclopentadienes when 2 equiv of nitriles were added and the resulting two-carbon unit and three-carbon unit were converted into a benzene derivative and a pyridine derivative, respectively, in one-pot.     

Recent topics in annulation reaction via double CH bond cleavage and double CC bond formation

Cyclic compounds have been consistently key components in organo functional molecules. To construct cycles, a catalytic two CH bond-cleaving annulation is one of the most ideal and straightforward methods with atom and step economies. Recently, many patterns of such annulation reactions have been developed, which construct a variety of cyclic compounds consisted of from simple to complex frameworks. This Digest focuses a recent progress in two or more than three CH bond-cleaving annulation reactions and is outlined as follows: (1) intramolecular annulation, (2) intermolecular annulation via double CH bond cleavages in one molecule, and (3) intermolecular annulation via double CH bond cleavages in two molecules.     

Electrochemical cleavage of the double bond of 1-alkenylarenes

A study has been made of the electrochemical cleavage of the double bond of propenylbenzene (Ia) and p-propenylanisole (Ib), which takes place upon anodic oxidation of (Ia, b) in alcoholic solutions of sodium trifluoroacetate and other electrolytes and which leads to conversion of (Ia, b) to benzaldehyde dialkylacetals. Conditions are found that provide for highly selective (>80%) conversion of (Ib) and p-propenyl toluene to p-methyl- and p- methoxybenzaldehyde dimethylacetals.Translated from Izvestiya Akademii Nauk SSR, Seriya Khimicheskaya, No. 3, pp. 644–649, March, 1991.The authors want to thank I. V. Makhova for participating in the initial stage of the study and obtaining the preliminary experimental data about the possibility of electrochemical cleavage of the double bond of p-propenylanisole in an alcoholic solution.     

Carbon-carbon double bond cleavage with a hard lewis acid and ethanethiol

Double bonds activated by the electron withdrawing group(s) are cleaved with the reagent system consisting of a hard Lewis acid and ethanethiol to give dithioacetals.     

Gold(I)-catalyzed oxidative cleavage of a C-C double bond in water

[reaction: see text] Oxidative cleavage of the C=C bond to afford ketone or aldehyde products with tert-butyl hydrogenperoxide (TBHP) as the oxidant can be catalyzed by AuCl with neocuproine (1) in water.     

Reaction of a double bond of zirconacyclopentadienes: formation of 1,2,3,5-tetrasubstituted benzenes via the C-C bond cleavage.

Reactions of zirconacyclopentadienes with dichlorocarbene afforded cyclopropanation products in good yields. In a similar manner, reactions of zirconacyclopentadienes with a Simmons-Smith type cyclopropanation reagent also gave vinylcyclopropanes in good yields after hydrolysis. Before hydrolysis, the formation of 1-zirconabicyclo[3.1.0]hexene was observed by 13C NMR spectroscopy. The 1-zirconabicyclo[3.1.0]hexene deriatives reacted with CO to produce 1,2,3,5-tetrasubstituted benzene derivatives in good yields via the C-C bond cleavage of the cyclopropane rings. This is in sharp contrast to the formation of usual 1,2,3,4-tetrasubstituted benzene derivatives from zirconacyclopentadienes.     

Copper-catalyzed oxidative cleavage of carbon-carbon double bond of enol ethers with molecular oxygen

A novel CC bond cleavage reaction of aromatic enol ethers (1) to give ketones (2) using molecular oxygen as oxidant is described. Among the examined catalysts (Cu(II), Pd(II), Ru(II), and H⁺), CuCl₂ exhibited the highest activity. The reaction proceeded smoothly with several kinds of substrates.     

Unusual carboncarbon double bond cleavage in thiophenohomotropone system promoted by ethanedithiol

Non classical carboncarbon double bond cleavage in a homoaromatic system is initiated by ethanedithiol and p-toluenesulfonic acid. The structure of the unexpected product is proved by X-ray analysis. The proposed mechanism is supported by deuterium labelling experiments and common reactivity considerations.     

Microbial cleavage of CF bond

Fluorochemicals are gaining importance due to their stability, inertness and versatile applications. In the present paper, interactions of microorganisms with organofluorine compounds are reviewed with an intention of analyzing their ability to handle this specialized group of chemicals and to explore the potential of this knowledge in biotechnological applications. Thus an overview is given on the microbial cleavage of CF bond in aliphatics and aromatics.     

Metal-free, NHPI catalyzed oxidative cleavage of C-C double bond using molecular oxygen as oxidant

A metal-free N-hydroxyphthalimide (NHPI) catalyzed aerobic oxidative cleavage of olefins has been developed. Molecular oxygen is used as the oxidant and reagent for this oxygenation reaction. This methodology has prevented the use of toxic metals or overstoichiometric amounts of traditional oxidants, showing good economical and environmental advantages. Based on the experimental observations, a plausible mechanism is proposed.     

Aryl-oxygen bond cleavage by a trihydride-bridging ditantalum complex

We have described the synthesis of the cyclometalated trihydride ditantalum(V) complexes supported by the aryloxide tridentate ligand. According to variable-temperature NMR studies, these dimers could provide a masked form of Ta(IV)-Ta(IV) and/or Ta(III)-Ta(III). In addition, these complexes were found to undergo hydrodeoxygenation of the aryloxide ligand.     

Ruthenium-catalyzed alkoxylation of a hydrodisilane without SiSi bond cleavage

Transition metal-catalyzed synthesis of alkoxydisilanes via dehydrogenative coupling of a hydrodisilane with alcohols is reported. During the reaction, the SiSi bond is preserved effectively when [RuCl₂(p-cymene)]₂ is used as a catalyst. Various alcohols can be used in this alkoxylation.     

Sulfur and selenium ylide bond enthalpies

The bond dissociation enthalpies (BDEs) of sulfur and selenium ylides have been estimated by applying MP2/6-311++G(3df,2p)//MP2/6-31G(d,p), G3, and other computational methods. Computed sulfoxide bond enthalpies were compared to experimental results to ensure the reliability of the computational methods before extending to related compounds. The examined ylides include the following: sulfoxides, sulfilimines, S,C-sulfonium ylides, and selenoxides. Selenoxides have BDEs about 10 kcal/mol smaller than the corresponding sulfoxides. N-H sulfilimines and CH2-S,C-sulfonium ylides have low BDEs, unless the sulfilimine or S,C-sulfonium ylide is stabilized by an electronegative substituent on N or C, respectively. Incorporation of the S or Se into a thiophene or selenophene-type ring lowers the BDE for the ylide.     

Unexpected oxidation of a substituted benzo[a]phenazine: oxidative cleavage of a double bond and formation of a macrolactone

Peroxidation of the phenazine of β-lapachone using m-ClC₆H₄CO₃H/CH₂Cl₂ furnished a macrolactone with a rigid 10-membered ring, and the corresponding N-oxide, originating from the oxidative cleavage of the aromatic double bond at the site of fusion of the dihydropyrane moiety with the phenazine component. A third compound, a dihydrobenzophenazine-5-one, was also generated probably by hydrolysis of an intermediate epoxide-acetal or α-hydroxy-hemiacetal formed at the same site. All of the new compounds were fully characterized by X-ray diffractometry and spectroscopic methods.