Benzene reaction with isocyanides

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

This silylene formation from 27 under mild conditions permits the synthesis of a variety of interesting carbo- and heterocycles, most of which are new types of compounds. The results are summarized in Schemes 5 and 6. The reactions with benzene and naphthalene represent the first examples of [2+1] cycloadditions of a silylene with aromatic C=C double bonds.59 623 The reactions with carbon disulfide and isocyanide (Scheme 6) are also of great interest because of their unusual reaction patterns.62b... 

This reaction has been extended to photoassisted insertion of isocyanide into C-H bonds [62,63]. When the reaction of benzene with isocyanide was carried out with the aid of Fe(PMe3)2(CNCH2But)3 as the catalyst under irradiation conditions, the corresponding aldimine was obtained. Under dilute reaction conditions, the reaction became catalytic and efficient (Eq. 34). Tanaka and Sakakura have also reported photoassisted RhCl(CO)(PMe3)2-catalyzed insertion of isocyanide into C-H bonds in benzene and pentane, but the turnover number of the catalyst is not high (2.45 turnovers) [64]. 

Mono-axially coordinated species are most conveniently formed by the reaction of single face-hindered Fe(II) porphyrins with isocyanide in a non-coordinating solvent, such as toluene or benzene,or when four-coordinate PFe are reacted under an inert atmosphere with nitrogen bases, such as imidazoles and pyridines in the presence of isocyanide This... 

F 4] Cycloaddition with Vinyl Isocyanates. Upon thermolysis in refluxing benzene, 2,5-dihydro-2,2-dimethyl-5,5-bis-(propylthio)-l,3,4-oxadiazole yields the bis(propylthio)carbene precursor, which reacts as a 1,1-dipole equivalent in [1 -E 4] cycloaddition reactions with various vinyl isocyanate substrates leading to highly functionalized adducts such as hydroindolones (eq 1). Reductive desulfurization with Raney nickel yields the enamide or the fully reduced system (eq 2). Cyclohexyl isocyanide also behaves as a 1,1-dipole equivalent in [1 -E 4] cycloadditions with vinyl isocyanates, however the adducts are less functionahzed. ... 

The cyclopentadienyl ligand of titanocene serves as a five-carbon source for the benzene ring in the reaction with the enal 113 (Scheme 7.44) [62]. Initially, the enal 113 was treated with Cp2Ti(PMe3)2 to form the oxatitanacycle 114. n-Butyl isocyanide was then inserted into the C-Ti bond of 114 and subsequent reductive elimination afforded 115. Subsequent treatment with 1N HCl generated cyclopentane 116. 

In a related reaction, isocyanides can be converted to aromatic aldimines by treatment with an iron complex followed by irradiation in benzene solution RNC -I- CftHe PhCH=NR. ... 

For each of these reactions kinetic data were obtained. The reactions were first order in complex concentration, and zero order in isocyanide, as expected. The complex Ni(CNBu )4, and presumably other Ni(CNR)4 complexes as well, undergo ligand dissociation in solution. In benzene solution, a molecular weight determination for this compound gives a low value (110). This is in accord with the presumed mechanism of substitution. 

The use of a pyrimidine precursor continues to be the more popular approach to furo pyrimidines. The one-pot three-component condensation reactions of alkyl or aryl isocyanides with A[A -dimethylbarbituric acid in the presence of terephthaldialdehyde proceeded spontaneously at room temperature in DMF to give good yields of the corresponding l,4-bis(6-alkyl or arylamino-1,3-dimethylfurano[2,3-4]pyrimidin-2,4(l//,3//)-dione-5-yl)benzenes <2006BMCL3697>. 

A number of indoles of type 315 have been made (80TL281 83JOC3639) by stirring f-butyl and some other isocyanides in benzene or acetonitrile with various arylnitropropenes (314), and the reaction is thought to proceed as indicated. 5-,6-, and 7-Substituted and benzole]- and -[g]-l-hydroxyindoles have also been obtained yields varied from 15-87%. 

Imidoyl radicals are often prepared by the addition of carbon- or heteroatom-centred radicals to isocyanides, but can also be prepared by hydrogen atom abstraction from imines. This latter method has been adopted in a new annulation approach to quinoline synthesis. Thus, reaction of the imine 1 with phenylacetylene and di-isopropyl peroxydicarbonate in benzene at 60°C gave a mixture of the quinolines 2 and 3 in 65% yield (2 3 = 4.4). 

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