Carbenes copper chloride

Photochemical decomposition of diazo(trimethylsilyl)methane (1) in the presence of alkenes has not been thoroughly investigated (see Houben-Weyl Vol. E19b, p 1415). The available experimental data [trimethylsilylcyclopropane (17% yield) and la,2a,3/J-2,3-dimethyl-l-trimethylsilylcyclopropane (23% yield)] indicate that cyclopropanation occurs only in low yield with ethene and ( )-but-2-ene.24 In both cases the formal carbene dimer is the main product. In reactions with other alkenes, such as 2,3-dimethylbut-2-ene, tetrafluoroethene or hexafluoro-propene, no cyclopropanes could be detected.24 The transition-metal-catalyzed decomposition of diazo(trimethylsilyl)methane (1) has been applied to the synthesis of many different silicon-substituted cyclopropanes (see Table 3 and Houben-Weyl Vol.E19b, p 1415).3-20a b-11 Copper chloride has been most commonly used for carbene transfer to ethyl-substituted alkenes, cycloalkenes, styrene, and related arylalkenes.3,203,15,21 25 For the cyclopropanation of acyl-substituted alkenes, palladium(II) chloride is the catalyst of choice, while palladium(II) acetate was less efficient, and copper chloride, copper(II) sulfate and rhodium(II) acetate dimer were totally unproductive.21 The cyclopropanation of ( )-but-2-ene represents a unique... 

ABSTRACT. Lithiumthiazoles react by substitution or addition with gold and copper chlorides and subsequent protonation or alkylation affords stable mono- or bis(carbene) complexes. Complications which occur during these syntheses include homoleptic rearrangement, dissociative polymerization and carbon-carbon ligand coupling. 

The same lithium salts with copper(I) chloride react through the stage of the anionic C-coordinated complexes 100, which on protonation with hydrochloric acid give the corresponding 2,2 -bithiazoles, with triflic acid— the N-coordinated species 101, and on methylation with methyl triflate they give carbenes of structure 102. 

Transfer of carbene 3a from 19 to a variety of alkenes and cycloalkenes has been achieved under catalysis by copper(I) chloride74,79 - 82. However, with the exception of cyclohexene69,70 (72% yield), only moderate yields could be obtained. In all cases, the cyclopropanation was stereospecific with respect to the double bond configuration of the alkene and gave the sterically less crowded cyclopropane diastereomer in excess. As in the photochemical cyclopropanation, the formal carbene dimer trans-1,2-bis(trimethylsilyl)ethene is often formed as the major by-product. Cyclopropanation of fraws-but-2-ene with 19 with copper(II) chloride as catalyst was found to be even less... 

For alkyl(silyl)carbenes where the alkyl contains an a-C—H bond, 1,2(C C) hydride shift leading to a vinylsilane is the common reaction pathway. Vinylsilane formation has been observed for free (photochemically or thermally generated) carbenes (equations 4384, 4448.49.50 and 45 85,86) but also in carbenoid reactions. In the latter case, the configuration of the alkene could be controlled to a large extent by the choice of the catalyst The -alkene was formed nearly exclusively with copper(I) chloride as catalyst87, whereas rhodium(II) pivalate88 gave mainly the Z-alkene (equation 46). 

Arnold and co-workers also reported the deprotonation of alkoxy imi-dazolium iodides with -butyl lithium to yield lithium alkoxide carbenes (Scheme 3).14 Single crystals of one of the complexes were grown from a diethyl ether solution, and revealed a dimer of LiL with lithium iodide incorporated to form a tetramer of lithium cations (7). The lithium-NHC bond distance of 2.131(6) A is similar to that of the lithium amide carbene 4. Also as in 4 there is distortion of the lithium-NCN bond which has an angle of 152.3°. The C2 carbon resonates at 200 ppm in the 13C NMR spectrum which is a relatively high-frequency, possibly as a result of the incorporated lithium iodide. The lithium salts were able to act as ligand transfer reagents and react with copper (II) chloride or triflate to afford mono- or bis-substituted copper(II) alkoxy carbene complexes. 

Ylide (45, X = CH2) reacts with a number of alkyl and aryl alkynes, in the presence of copper(I) chloride as catalyst, to form bicyclic furan derivatives (equation 52) . This reaction probably involves a carbene as intermediate. 

Poly(l,4-butadiene) segments prepared by the ruthenium-mediated ROMP of 1,5-cyclooctadiene can be incorporated into the ABA-type block copolymers with styrene (B-106) and MMA (B-107).397 The synthetic method is based on the copper-catalyzed radical polymerizations of styrene and MMA from the telechelic poly(butadiene) obtained by a bifunctional chain-transfer agent such as bis(allyl chloride) or bis-(2-bromopropionate) during the ROMP process. A more direct route to similar block copolymers is based on the use of a ruthenium carbene complex with a C—Br bond such as Ru-13 as described above.67 The complex induced simultaneous or tandem block copolymerizations of MMA and 1,5-cyclooctadiene to give B-108, which can be hydrogenated into B-109, in one pot, catalyzed by the ruthenium residue from Ru-13. 

In contrast to these examples, decomposition of 3-diazo-2-oxobicyclo[2.2.2]octane results mainly in the Wolff rearrangement product rather than in /S-C-H insertion (3-oxotri-cyclo[2.2.2.0 ]octane, 5%), Similarly, the 1,3-cyclization of the carbene derived from 2,2,5,5-tetramethyl-4-diazo-3-hexanone (5) by thermal, photochemical or copper(I) chloride catalyzed decomposition leading to 7 is far less efficient than a 1,2-methyl shift. ... 

A large variety of codimerization reactions under the catalytic action of copper complexes is known. Usually, these reactions proceed via carbene intermediates and provide substituted ethenylcyclopropanes. Most of the catalysts for these reactions consist of copper(I) chloride and a phosphorus ligand, such as triphenylphosphane or triphenyl phosphite. Under the influence of these catalysts, carbenes are presumably formed from various substituted cyclopropenes at temperatures ranging from —40 to - -20°C, and these carbenes can be trapped by reaction with alkenes. ... 

The reaction of 3,3-disubstituted cyclopropenes with mono- and 1,2-disubstituted alkenes proceeds only with difficulty and leads to low yields of cyclopropanes. In the case of but-l-ene, an 8% yield, with hex-1-ene and hept-l-ene between 5 and 10% yield, and with cyclooctene about 10% of the cyclopropane product is formed. In these cases, the major product is the formal dimer of the intermediate ethenylcarbene complex, i.e. the corresponding (fj-hexatriene. When copper(I) chloride is used as catalyst rather than the copper halide/phosphane or phosphite system, about half the yield of the [2-f-1] cycloadduct is obtained along with an increased amount of the hexatriene. Mechanistically, these acyclic trienes could also be formed from an (alk-l-enyl)bicyclo[1.1.0]butane intermediate without any carbene being involved. Bicyclo[1.1.0]butanes are low yield (< 20%) byproducts of the thermal dimerization reaction of methyl 3,3-dimethylcyclopropenecarboxylate (1). On the other hand, bicyclo[l. 1. Ojbutanes, such as 3, are known to undergo isomerization to form 1,3-dienes. ... 

As this stereochemical outcome is comparable to that obtained with the Simmons-Smith reagent or diazomethane in the presence of copper(l) chloride, the intermediacy of carbenes or car-benoids can be assumed. " The exo,anti-product is favored over the xp,5y -compound in both cases. 

With copper(I) chloride as catalyst, 3-anf/-(2-methoxycarbonyl-l-methylethenyl)-cxo-tricyclo[3.2.1.02,4]oct-6-ene (8, R = Me) and 3-an//-[l-(methoxycarbonylmethylene)butyl]-e,xo-tricyclo[3.2.1,02,4]oct-6-ene (8, R = Ph) are isolated in 70 und 60% yield, respectively, and in a ZjE isomeric ratio of 1.3 1 and 1.7 1 after preparative thin layer chromatography.63a,b As this stereochemical outcome is comparable to that obtained with the Simmons-Smith reagent or diazomethane in the presence of copper(l) chloride, the intermediacy of carbenes or car-benoids can be assumed.64 The exo,anti-product is favored over the uxo,sy -compound in both cases. 

Cyclopropanation. In the presence of copper powder the reagent decomposes to the carbene CHP(=0)(0CH3)2, which adds to double bonds. Methylene chloride is the preferred solvent. 

A more efficient preparation of 7-(trimethylsilyl)bicyclo[4.1.0]heptane employs (trimethylsi-lyl)diazomethane under copper(I) chloride catalysis7. This method also allows the synthesis of l-phenyl-2-(trimethylsilyl)cyclopropane with good tram preference8. For silyl and related carbenes see Vol.E19b. pp 1410-1459 and for the synthetic uses of silyl-substituted cyclopropanes see reference 9. 

The bismuthonium ylide 519 is converted into the annelated furans 522 on treatment with terminal alkynes in the presence of copper(I) chloride. It is suggested that the process involves the carbene 520 and the diradical 521. Intramolecular [2 + 2 + 2] cycloaddition of the triyne 523 mediated by tris(triphenylphosphine)rhodium(I) chloride gives the tetrahydrofuranobenzofuran 524. ... 

The carbenes or carbenoids can be generated in a variety of ways. It is not always clear whether the reaction is concerted or stepwise and whether the carbene behaves as an electrophilic, nucleophilic or radical species. For instance, a carbenoid generated from bismuthonium ylide (19) in the presence of copper(I) chloride would behave as a triplet and add as a radical to a terminal alkyne" (equation 17). The dicarbonyl structure and the absence of reaction with methyl propionate to a furane might well indicate electrophilic character of this carbene. 

Addition of carbenes to aromatic systems leads to ring-expanded products. Methylene itself, formed by photolysis of diazomethane, adds to benzene to form cycloheptatriene in 32% yield a small amount of toluene is also formed by an insertion reaction. The cycloheptatriene is formed by a Cope rearrangement of the intermediate cyclopropane (a norcaradiene). More satisfactory is the reaction of benzene with diazomethane in the presence of copper salts, such as copper(I) chloride, which gives cycloheptatriene in 85% yield (4.87). The reaction is general for aromatic systems, substituted benzenes giving mixtures of the corresponding substituted cycloheptatrienes. 

We have also undertaken a study involving the synthesis of diaminocarbene complexes of copper and we succeeded in preparing and characterizing a neutral chloride-bridged carbene complex derived in a similar manner as before from N-methylimidazolyllithium, CuCl and CF SO Me. It decomposes, however, much easier than its... 

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