Benzene carbene insertion into

Substituted diazomethanes, such as diazoacetic ester, react with some arylcopper compounds 34, 255) by carbene insertion into the C—Cu bond [Eq. (34)]. Isonitriles are also reported 281d) to insert into an aryl—Cu bond [Eq. (35)] in benzene solution at 25°C. 

Dias et al. (132) and Lovely et al. (133) also used the system shown above to catalyze carbene insertion into both saturated C—H bonds and aromatic rings. Ethers and substituted benzenes gave lower yields than aliphatic hydrocarbons and benzene. The carbene insertion into aromatic rings is generally two to seven times faster than the insertion into aliphatic C—H bonds (Fig. 29). 

The first phosphonia-alkene (155) has been prepared as shown an X-ray crystal structure reveals a twist of 60° around the double bond The diphosphino-diazomethane (156) upon heating in benzene gave (157) by carbene insertion into one of the isopropyl groups. The first diphosphirene (158) has been prepared and... 

When the ketone contains a bulky group, such as t-butyl, a TMS containing alcohol is obtained instead of a disubstituted hydrocarbon. If the solvent is changed from HMPT to tetramethylurea (TMU), the aryl ring is silylated and a ketone is isolated [88]. When less than 2 Eq of TMSCl are employed, the reaction products contain no silane species. The cyclopropyl and ethylenic benzene derivatives are postulated to arise from a carbene insertion into the f-Bu group and a Me group rearrangement [88]. 

Thermal decomposition of 2-diazohexafluoropropane, or 2-diazo-3,3,3-trifluoro-propanenitrile in excess benzene (150-200 "C, autoclave) resulted in efficient cyclopropanation of an aromatic C-C double bond. In solution, the 7-trifluoromethylnorcaradiene 9 (-bicyclo[4.1.0]hepta-2,4-diene) so formed is in rapid valence equilibrium with the corresponding cycloheptatriene 10 however, this equilibrium is shifted predominantly or completely to the cycloheptatriene side. As a byproduct in the synthesis, the product of carbene insertion into an aromatic C-H bond is obtained. An experimental procedure for the synthesis of 10b can be found in Houben-Weyl, Vol. 19 b, p 1031. 

Cycloaddition with Vinyl Isocyanate. When a large excess of 2,5-dihydro-2,2-dimethyl-5,5-bis(propylthio)-1,3,4-oxadiazole carbene precursor is added rapidly in refluxing benzene to a vinyl isocyanate, two equivalents of carbene add to the substrate prior to ring closure, leading to a six-membered adduct (eq 3). However, no carbene insertion into the amide N-H bond occurs. This phenomenon is not observed with the dimethoxy carbene. ... 

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

Laser flash photolysis of phenylchlorodiazirine was used to measure the absolute rate constants for intermolecular insertion of phenylchlorocarbene into CH bonds of a variety of co-reactants. Selective stabilization of the carbene ground state by r-complexation to benzene was proposed to explain the slower insertions observed in this solvent in comparison with those in pentane. Insertion into the secondary CH bond of cyclohexane showed a primary kinetic isotope effect k ikY) of 3.8. l-Hydroxymethyl-9-fluorenylidene (79), generated by photolysis of the corresponding diazo compound, gave aldehyde (80) in benzene or acetonitrile via intramolecular H-transfer. In methanol, the major product was the ether, formed by insertion of the carbene into the MeO-H bond, and the aldehyde (80) was formed in minor amounts through H-transfer from the triplet carbene to give a triplet diradical which can relax to the enol. 

In a similar study, arc generated atoms were allowed to react with tert-butyl-benzene in order to use the tert-butyl group as an intramolecular trap for the carbene. This reaction gave drmethylindane-3- C (56) and 3,3-dimethyl-3-phen-ylpropene-l- C (57). The label distribution in 56 indicates that it arises from an initial insertion into an ortho C H bond to give o-tert-butylphenylcarbene (58), whUe 57 results from insertion into a methyl group C—H (Eq. 35). The fact that... 

P-Lactams,2 Decomposition of N-benzyl-N-r-butyldiazoacetoacetamide (1) with Rh2(OAc)4 in refluxing benzene results iti the P-lactam 2 in 98% yield. The acetyl group on the diazo carbon is necessary for this insertion into the p-C—H bond rather than reaction of the carbene with the aromatic ring. The /-butyl group... 

In the next step, 3 could insert into one of the C H bonds of 1 to provide vinylacetylene (4, butenyne), a compound that is indeed generated when 1 is pyrolyzed. Repetition of the carbene formation step could then produce 5, which, by another insertion step, would lead to hexa-l,3-dien-5-yne (6, mixture of isomers). This is already an isomer of benzene, and that it can cyclize to 2 was shown by us many years ago [6]. Obviously, 6 could also be a precursor of styrene and other oligomers of 1. The mechanism proposed in Scheme 2 could also be of importance in connection with soot formation from smaller hydrocarbon fragments, and account for the formation of 2 in interfeller space. 

A review has discussed the photochemical cyclization of a variety of aryl- and heteroaryl-prop-2-enoic acids. Irradiation (A,>340nm) of the cyclohexenone (119) in argon purged benzene solution affords the cyclized derivatives (120) as a 3 1 mixture of diastereoisomers. The formation of the cyclopropyl group arises via the carbene (121) and insertion into a C-H bond of a neighbouring methyl group. This carbene is formed, presumably, from the biradical (122) which arises by addition of the alkene to the excited state of the enone. Further evidence for the carbene intermediate comes from a reaction in methanol when the diastereo-isomeric mixture of the ethers (123) and (124) is obtained." ... 

In contrast, 13C-labeled phenyl(3-pyridyl)carbene (285) rearranged to a 1- and 3-azafluorene by virtually exclusive insertion into the benzene ring (Eq. 82).232... 

Vinylsilanes have also been prepared from the same precursors. Thus treatment of (1), R = CHj, with lithium ethoxide (1, 612-613) in benzene containing triethylsilane gives triethyl (2-methyl-l-propenyl)silane (5) in 61% yield. Since carbenes are known to insert into the SiH bond, an unsaturated carbene (4) is apparently involved.2... 

Laser flash photolysis of phenylchlorodiazirine was used to measure the absolute rate constants for intermolecular insertion of phenylchlorocarbene into CH bonds of a variety of co-reactants. Selective stabilization of the carbene ground state by r-complexation to benzene was proposed to explain the slower insertions observed in this solvent in comparison with those in pentane. Insertion into the secondary CH bond of cyclohexane showed a primary kinetic isotope effect k ikY) of 3.8. 

In one of the stages of the reaction between carbon atoms and terf-butyl-benzene, a carbon atom inserts into a methyl C-H bond to give a carbene followed by a 1,2-hydrogen shift (Scheme II.2) [8b]. 

The formation of toluene in the reaction of diazomethane with benzene (8-3) brings us to the second characteristic reaction of carbenes, namely insertion into single bonds, in this case into an sp -C —H bond. Here again prehistoric examples (i.e., investigations before 1950) of Buchner and Meerwein are known (Buchner and Schulze, 1910 Buchner and Scholtenhammer, 1920 Meerwein et al., 1942), as well as early systematic work by Doering s group after 1950. 

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