Carbene, Dichloro

Polyisoprenes and polybutadienes can also be modified by reactions with carbenes. Dichloro-carbene adds to natural rubber dissolved in chloiofoim in a phase transfer reaction with aqueous NaOH and a phase transfer reagent. Solid sodium hydroxide can be used without a phase transfer reagent. There is no evidence of cis-trans isomerization and the distribution of the substituents is random. ... 

Ci5H2 Fi2N60P2Pd2, Hexakis(methyl isocyanide)dipalladium(I) hexafluorophosphate acetone solvate, 41B, 831 C15H2 eCl2NOPPt, cis-(Anilino(ethoxy)carbene)dichloro(triethylphos-phine)platinum(II), 42B, 617... 

Cl 8H2 2M0NO5P, (r -N-Phenyliminoethyl) (rj -cyclopentadienyl) (trimeth-ylphosphite)dicarbonyImolybdenum, 44B, 745 Cl8H23Cl20PPt, cis-[Benzyl(ethoxy)carbene]dichloro(dimethylphenyl-phosphine)platinum(II), 45B, 854... 

Apparatus 250-ml three-necked flask (see Pig. 1) for the addition of dichloro-carbene and the dechlorination. 

The only known reaction of a furan with a dihalocarbene is that recently reported between benzofuran and dichlorocarbene in hexane at 0°. The initial adduct (7) could not be isolated but on hydrolysis gave the ring-expanded product 8, possibly via 9, in 15% yield. Benzothiophene was recovered in 92% yield under the same conditions. 2,5-Dihydrofuran reacted with dichloro- and dibromo-carbene to give the products of allylic insertion, 2-dihalogenomethyl-2,5-dihydrofuran, as well as the normal addition products. ... 

However, the presence of a fused benzene ring was found to hmit the scope of this type of ring expansion severely. Thus the dichloro-carbene adducts of both 2H- (33) and 4H-chromen (34) failed to rearrange to 2,3-benzoxepines (35) on heating. Although some... 

The versatile starting material lCp RuCI 4 (1) reacts rapidly with sterically demanding phosphines (PCy and P Pr ) as well as with the nucleophilic carbene ligands (L) to give deep blue, coordinatively unsaturated Cp Ru(L)CI complexes 2-8 (L= l,.Tbis(2,4,6-lrimethylphenyl) (IMes. 2) 1,3-R2-imidazol-2-ylidene = cyclohcxyl (ICy, 3) 4-methylphenyl (ITol, 4) 4-chlorophenyl (IPCl, 5) adamanlyl (lAd, 6) 4..5-dichloro-1,3-bis(2.4,6-trimethylphenyl) (IMesCI, 7) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenc (IPr. 8) in high yields according to Eq. (4). 

According to the matrix IR spectra, the preferred formation of dichloro-carbene along with SiCU (1 3 60()-620cm ) or GeCU (1 3 445-465 cm ) has been also observed under vacuum pyrolysis (500-1000°C, 10 -10 Torr) of trichloromethyltrichlorosilane and trichloromethyltrichlorogermane (Scheme 3). The CCI3 radical was formed in substantially lower amounts (Svyatkin et al., 1977 Nefedov et al., 1976). 

Cyclopropylchlorocarbene [20] has been generated by UV photolysis (A = 335 nm) of cyclopropylchlorodiazirine [21] frozen in a nitrogen matrix at 12 K (Ho et al., 1989). IR and UV spectra of [20] have been recorded. The reaction of [20] with HCl resulted in the formation of (dichloromethyl)-cyclopropane [22], and annealing of the matrix gave (dicyclopropyl)dichloro-ethene [23]. Subsequent irradiation (A = 450 nm) of the carbene [20] led to its isomerization to 1-chlorocyclobutene [24], which was partialy destroyed to give ethene and chloroacetylene. Ab initio calculations predict the existence of two carbene conformers, but attempts to distinguish them in IR or UV spectra were unsuccessful. 

An important synthetic application of this reaction is in dehalogenation of dichloro- and dibromocyclopropanes. The dihalocyclopropanes are accessible via carbene addition reactions (see Section 10.2.3). Reductive dehalogenation can also be used to introduce deuterium at a specific site. The mechanism of the reaction involves electron transfer to form a radical anion, which then fragments with loss of a halide ion. The resulting radical is reduced to a carbanion by a second electron transfer and subsequently protonated. 

The elongated dihydrogen complex OsCl2(r 2-H2)(CO)(P,Pr3)2 reacts with phenylacetylene to give the dichloro-carbene derivative OsCl2(CHCH2Ph)(CO) (P Pr3)2 (Eq. 6), which has been characterized by X-ray diffraction analysis.35... 

The reactivity of dichloro carbene towards acetylenic bonds was systematically investigated by Dehmlow19, 20 with respect to substitution of the acetylene, especially those containing additional C-C multiple bonds. It was shown that with aiyl alkyl acetylenes, e.g. 1-phenyl-butyne-l, often the normal cyclopropenone formation occurs only to a minor extent (to yield, e.g. 14), whilst the main reaction consists of an insertion of a second carbene moiety into the original acetylene-alkyl bond (giving, e.g. 15) ... 

At 62% yield, the main product of the reaction of 42b with MeLi (molar ratio 1 5.5) was l,2-dichloro-2-methylbicyclo[2.1.1]hexane (66). Again, the most probable mechanism leading to 66 is addition of MeLi to carbene 54 (X=H, X=C1), followed by lithium chlorine exchange of the intermediate tertiary alkyllithium base 67 with the trichloride 42b. An alternative mechanism, addition of LiCl to carbene 54 and methylation of the intermediate carbenoid by MeLi, formed during the reaction from MeLi and 42b, is less probable.24... 

The first fraction, b.p. 55-58° (1 mm.) is isotetralin ( 50 g.) (Note 16). Some more of this material distills when the column is heated to about 100°. The temperature in the head of the column thereby rises to 90-95°, and it is then necessary to change the receiver flask. The second fraction, b.p. 95-102° (1 mm.) constitutes the 1 1-adducts of dichloro-carbene to isotetralin ( 108g.), which consist of 92% of 11,11 -di-chlorotricyclo[4.4.1.01,6]undeca-3,8-diene and 8% of the side-addition product. The residue mainly contains the 2 1-adducts. The fraction of the 1 1-adducts is recrystallized from methanol (about 500 ml.) to give 87-97 g. (40-45%, based on isotetralin initially used) of 11,11-dichlorotricyclo[4.4.1.01,B]undeca-3,8-diene as long colorless needles, m.p. 88-89° (Note 17). 

Chloro(phenylthio)carbene [32] has been produced by the standard phase-transfer catalytic procedure from PhSCHCK and trapped by alkenes (see Section 7.3), although the carbene is also prone to dimerization to give [PhS(Cl)C=C(Cl)SPhj. In a similar manner, phenylthiocarbene has been obtained from PhSCH2Cl [33] and chloro(phenoxy)carbene from dichloro(phenoxy)methane [34]. Reaction of the analogous seleno derivatives produce the conesponding phenylselenocarbenes... 

Chloro(methylthio)carbene is generated from dichloro(methylthio)methane... 

Cycloocta-2,5-diene yields the mono adduct with dimethylvinylidene carbene ( 19%) [156]. With dichloro- and dibromocarbene, the syn- and cmh-bis-adducts are obtained in a ratio which favours the syn-isomer [55, 104] whereas, with bromochlorocarbene, the mono-adduct is reported to be the major product (55%) with only 9% of the bis-adduct [142]. In contrast, cyclo-octatetraene is converted into the mono-, syn-1,2 5,6-bis-, tris-, and tetra-adduct with dichlorocarbene depending on the reaction conditions [4, 17, 25, 55] and the 1,2 5,6-bis-adduct with... 

Conjugated dienes yield mono-adducts with dihalocarbenes at the more electron-rich C=C bond further reaction at the less reactive bond may also occur [e.g. 4,8,19, 23, 31, 37, 49, 62, 69, 94]. Cycloheptatriene yields the syn- and nnti-1,2 5,6-bis-adducts (14.5 and 22.9%) and the syn-1,2 5,6-ann -3,4-tris-adduct with dichloro-carbene [62], The facile reaction of cyclopropylethenes with dihalocarbenes produces dicyclopropyl compounds [53, 117]. Isoprene reacts with chloro(phenylthio)carbene across the more reactive 1,2-bond (51%) [146]. 

In reactions which have some analogy with the interaction of dichloro-carbene/trichloromethyl anions with ketones, 2-dichloromethyloxazolines yield chloro-oxiranes and a-chlorocarbonyl compounds (Scheme 7.18). The formation of the oxiranes is favoured with aldehydes and lower homologue ketones, whereas cyclic ketones and aryl ketones are converted preferentially into the a-chloro carbonyl derivatives [18]. 

Diazomethane is also produced in the reaction of acylhydrazines with dichloro-carbene, but the process is less efficient, as only one equivalent of diazomethane is produced from two equivalents of the acylhydrazine. However, the procedure provides a useful route to symmetrical AUV -diacylhydrazines (Scheme 7.25) [11],... 

The major product isolated from the reaction of secondary amines with dichloro-carbene the reaction under phase-transfer conditions is the A-formylamine [12-14], The isolated yields are considerably higher (Table 7.14) than those recorded for classical procedures and are not inhibited by steric effects [15]. Diphenylamine is converted into its A-formyl derivative in low yield by conventional procedures and, although application of the phase-transfer catalysed procedure increases the yields, the E- and Z-l,2-bis(diphenylamino)-l,2-dichloroethenes are also obtained as byproducts of the reaction [13],... 

Experimental Procedure 3.1.3. Preparation of a Ruthenium Carbene Complex from a Diazoalkane Dichloro-bis(tricyclohexylphosphine)benzylideneruthenium... 

When 2,2-dichloro-3-phenylpropanal 203 is subjected to standard reaction conditions with chiral triazolium salt 75c, the desired amide is produced in 80% ee and 62% yield Eq. 20. This experiment suggests that the catalyst is involved in an enantioselec-tive protonation event. With this evidence in hand, the proposed mechanism begins with carbene addition to the a-reducible aldehyde followed by formation of activated car-boxylate XLII (Scheme 32). Acyl transfer occurs with HOAt, presumably due to its higher kinetic nucleophilicity under these conditions, thus regenerating the carbene. In turn, intermediate XLin then undergoes nucleophilic attack by the amine and releases the co-catalyst back into the catalytic cycle. 

Yields of dichlorocyclopropanes from reaction of alkencs with dichloro-carbene generated at a lead cathode in dichloromethane containing tetxa-butylammonium bromide. Ref. [79]. 

The additions of difluorocarbene onto the bicyclopropylidene derivative 121 (Scheme 24) [116a], of dibromocarbene onto oligospirocyclopropanated bicy-clopropylidenes 56 [33,65] (66% yield) and 62 [117] (94% yield), of dichloro-carbene onto 56 [33] (90% yield), 28a [118] (38% yield) and 121 (99% yield) 1116a] as well as of chloro(phenylthio)carbene (90%yield) [33,1191,of bromo-... 

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