Carbene diphenyl

Evident cases of abstraction/recombination mechanism are observed with phenylsubstituted carbenes. Diphenyl-diazomethane, which is photolyzed to give the triplet diphenyl-carbene, very readily abstracts a hydrogen atom from the benzyl group of toluene. The primarily formed radicals can now recombine to give a formal "insertion product — 1,1,2-triphenylethane — or they can recombine to form 1,1,2,2-tetraphenylethane and 1,2-diphenylethane... 

After the initial claim of the synthesis of an oxirene (by the oxidation of propyne Section 5.05.6.3.1) this system reappeared with the claim 31LA(490)20l) that 2-chloro-l,2-diphenyl-ethanone (110) reacted with sodium methoxide to give diphenyloxirene (111), but it was later shown (52JA2082) that the product was the prosaic methoxy ketone (112 Scheme 97) (the formation of 111 from 110 would be an a-elimination carbene-type reaction). Even with strong, nonnucleophilic bases, (110) failed to provide evidence of diphenyloxirene formation (64JA4866). 

H-Pyran, 2-alkoxy-4-methyl-2,3-dihydro-conformation, 3, 630 4H-Pyran, 2-amino-IR spectra, 3, 593 synthesis, 3, 758 4H-Pyran, 4-benzylidene-synthesis, 3, 762 4H-Pyran, 2,3-dihydro-halogenation, 3, 723 hydroboration, 3, 723 oxepines from, 3, 725 oxidation, 3, 724 reactions, with acids, 3, 723 with carbenes, 3, 725 4H-Pyran, 5,6-dihydro-synthesis, 2, 91 4H-Pyran, 2,6-diphenyl-hydrogenation, 3, 777 4H-Pyran, 6-ethyl-3-vinyl-2,3-dihydro-reactions, with acids, 3, 723 4H-Pyran, 2-methoxy-synthesis, 3, 762 4H-Pyran, 2,4,4,6-tetramethyl-IR spectra, 3, 593 4H-Pyran, 2,4,6-triphenyl-IR spectra, 3, 593... 

These different catalysts were first tested in the desymmetrization of the achiral triene 63 (Scheme 40). The best enantioselectivities (up to 39%) were obtained with complexes 60b and 61c-d bearing carbene ligands derived from 1,2-diphenyl-1,2-diaminoethane (R = Ph). ligands derived from 1,2-diaminocyclohexane gave poor enantioselectivities (< 9% ee). Replacement of the mesityl group in complex 60b by o-methyl- or o-isopropylphenyl groups (complexes 61c-d) slightly increases the enantioselectivity (from 13... 

Whereas the Rh2(OAc)4-catalyzed addition of diazoalkanes to propargyl alcohols readily gives the insertion of the carbene into the 0-H bond, with only a small amoimt of cyclopropenation of the resulting propargylic ether [54] the 2-diazopropane 59 reacts at 0 °C with l,l-diphenyl-2-propyn-l-ol 62a in dichloromethane and exclusively gives, after 10 h of reaction, only the adduct 63a isolated in 75% yield and corresponding to the regioselective 1,3-dipolar cycloaddition of the 2-diazopropane to the alkyne C - C bond (Scheme 15). 

Insertion of a carbene unit into the N—H bond of primary or secondary amines by copper salt catalyzed decomposition of diazo compounds has been known for a number of years14). The copper chelate promoted reaction of diazodiphenyl-methane 291) or 2-diazo-1,2-diphenyl-1-ethanone 292) with primary benzylamines or... 

The first synthesis of a cyclopropenone was reported in 1959 by Breslowls who achieved the preparation of diphenyl cyclopropenone (11) by reacting phenyl ketene dimethylacetal with benzal chloride/K-tert.-butoxide. The phenyl chloro carbene primarily generated adds to the electron-rich ketene acetal double bond to form the chlorocyclopropanone ketal 9, which undergoes 0-elimination of HC1 to diphenyl cyclopropenone ketal 10. Final hydrolysis yields 11 as a well-defined compound which is stable up to the melting point (120—121 °C). 

Independently Volpin17 synthesized diphenyl cyclopropenone from diphenyl-acetylene and dibromo carbene (CHBr3/K-tert.-butoxide). This reaction principle of (2 + 1) cycloaddition of dihalocarbenes or appropriate carbene sources ( caibenoids ) to acetylenic triple bonds followed by hydrolysis was developed to a general synthesis... 

Me Capra in particular proposed n> that the chemiluminescence reactions of a large number of organic compounds had this concerted dioxetane decomposition step as key reaction in the production of electronically excited products, namely acridinium salts 25,26,27) indolylperoxides 28>, activated oxalic esters 29>, diphenyl carbene 30>, tetrakis-dimethylamino-ethylene 31 32>, lucigenin 33>, and substituted imidazoles 23>. 

The optical spectrum of a triplet aromatic carbene can be recorded at low temperature and generally consists of two or more absorption bands. The position of these bands is often similar to the closely related transitions found in the correpsonding radical (Trozzolo and Gibbons, 1967). For example, DPM has absorptions with maxima near 300 and 465 nm and the diphenyl-methyl radical exhibits maxima at 336 and 515 nm (Porter and Strachan, 1958). 

Scheme 6.115 Generation of 1,3-dimethyl- (567) and 1,3-diphenyl-l, 2,4,6-cyclo-heptatetraene (572) and their ability to rearrange to a carbene even in solution.

Hegedus and co-workers8 reported the synthesis of (4S,5R)-4,5-diphenyl-3-vinyl-2-oxazolidinone (the enantiomer of the compound prepared here) via the chromium carbene complex in a fair yield. This is an interesting method, but the procedure is complicated (e.g., low temperature, argon atomsphere) and the chromium waste must be disposed of in an appropriate way. On the other hand, this procedure, consisting of transacetalization9 and pyrolysis,10 is simple and safe. Optically active 3-vinyl-2-oxazolidinone is also used for the synthesis of (1 R,2S)-2-fluorocyclopropylamine11a b that is the key intermediate for novel antibacterial quinolonecarboxylic acids. 

In 1981, Appel et al. postulated the transient formation of the (diphenyl-phosphino)(trimethylsilyl)carbene 2e to explain the formation of the phos-phaalkene 4e, in the thermolysis of the P-chloromethylene phosphorane 3e.29 At that time, the authors did not recognize the carbene character of 2e and simply named the intermediate a A5-phosphaalkyne. 

Carbonyl insertions into metallocarbenes have previously been observed for several different metals, including iron48 (see Section VI,C) and manganese.49 Indeed, carbonyl insertions into chrominum and tungsten diphenyl-carbenes have been shown to be viable processes.50 Most importantly, Wulff has isolated51 an 774-vinylketenecobalt (I) complex from the reaction between a cobalt carbene and an acetylene, a transformation that necessitates such a carbonyl insertion (see Section V,B). 

Kinetic studies of the thermolysis of diazomethane were carried out by various authors. These experiments demonstrated that the decomposition of diazomethane was a first order reaction 41-43) Similar investigations of the p5n olysis of diphenyl-diazomethane in xylene or 1-methylnaphthalene also showed that the disappearance of diphenyl-diazomethane is a first order process. It may be concluded that a free carbene is involved in these reactions, in accordance with the following scheme ). 

ENDOR (electron nuclear double resonance) studies of diphenyl-carbene indicated a dihedral angle of 34° for this species >. 

Flash photolysis of 5-diazo-lO, ll-dihydro-dibenzo[a, d]cycloheptene (75) — which can be regarded as a bridged diphenyl-carbene — at room temperature in hquid paraffin first produced the spectrum of the triplet carbene 16, which then disappeared to give the electronic spectrum of the radical 17. The latter finally gave the dimer 5,5 -bi (10, ll-dihydrodibenzo[a, djcycloheptenyl) 18 2). 

The photolysis of diphenyl-diazomethane in cis-jS-deutero-styrene, on the other hand, can be affected by dilution with hexafluorobenzene. The amount of trans-cyclopropane 49 is slightly larger, indicating that about 12% of the singlet carbene are still present in very dilute solutions (see Table 9). 

Table 9. Stereochemistry of addition of diphenyl-carbene to styrene as a function of added hexa-flurobenzene...

This degenerate rearrangement has not been observed with 5-dia-zomethyl-l,4-diphenyl-l,2,3-triazole. The diazo function decomposes and the carbene formed reacts, when benzene is used as solvent, into a cyclo-heptatriene. The requirement to have the ester function present at C-4 apparently has to do with stabilization of the diazo function. 

When 1-alkoxy- or 1,1-dialkoxycarbonylbenzocyclopropenes are photolyzed or heated above their melting points, furans may be formed via intramolecular interception of the intermediate carbenes. For example, 1,1-dimethoxycar-bonyl-2,5-diphenylbenzocyclopropene (263) reairanges at 170-210 °C to the fiiran 370. Similar reactions occur with 1,1-diphenyl-substituted benzocyclopropenes, which react to give fluorenes. ... 

Diazomethyl)-1,4-diphenyl-1,2,3-triazole (354) reacts with 1,4-disubstituted benzenes or naphthalenes to give a mixture of carbene derived norcaradiene/cycloheptatriene products (355) and (356) (Scheme 68). Attack is favored adjacent to the more highly branched substituent. When R = = Pr, a mixture of triazole derivatives (357) and (358), formed by addition to benzene and... 

The search for stable diaminocarbenes dates back to the early 1960s and is associated with the name of Wanziick." At that time the preparation of the 1,3-diphenyl imidazolidin-2-ylidenes (Ilia) was first examined (Scheme 8.4). Precursors of Ilia included the dimeric and electron-rich olefin IIIa 2 and the chloroform adduct 3a of the desired carbene. By means of cross-coupling experiments, however, it was shown that IIIa 2 was not in equilibrium with the two carbene units. On the other... 

Mamantov A. 1985. Tire photolysis of polychlorinated diphenyl ethers and chloroanisoles may proceed via carbenes. Chemosphere 14(6/7) 905-908. 

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