Bis-ketenimines

An eight-membered cyclic 7,./V-bis(germadiyl)bis(ketenimine) 190 was prepared by the reaction of tert-butyl-lithium with (fluorodimesitylgermyl)phenylacetonitrile 188 leading to the lithium salt 189, which then underwent an elimination of lithium halide. Compound 190, the first ring containing two ketenimine moieties, was characterized by IR and 13C NMR spectroscopy as well as X-ray structure determination (Scheme 34) <19980M1517>. 

In the 2001 communication [32] the cyclobutadiene 13 made from the cyclo-propene 14 was contaminated with the bis(ketenimine) 16, which complicated positive identification of the tetrahedrane 12 formed when the when the (impure) 13 was photolyzed. The use of pure 13 [34], readily available from the dianion, starting with bis(trimethylsilyl)ethyne and CpCo(CO)2 or CpCo(H2C=CH2)2, facilitated the preparation and identification of the tetrahedrane [33],... 

The reaction of bis-iminophosphoranes 328 with diphenylketene affords the bis-ketenimines 329 in high yields via [2+2] cycloaddition and cycloreversion processes... 

An intramolecular ketenimin-ketenimine [2+2] cycloaddition reaction has also been observed. The bis-ketenimine 57 was generated in situ by the aza-Wittig reaction and intramolecular cyclization afforded azeto[2,l-b]quinazolines 58 in moderate to good yields." ... 

A substituent in the 2-position of one of the aryl groups in the azobenzene gives rise to the formation of only the isomer 62 due to steric hinderance also, a p-dialkylamino group favors the formation of 62 due to the electronic effects. Bis-ketenimines form... 

Also, an intramolecular ketenimine-ketenimine [4+2] cycloaddition reaction is observed on heating the bis-ketenimine 175, generated in situ, to give the tetracyclic compound 176 in 64 % yield. ... 

StericaHy hindered or very electrophilic substituted ketenes, such as diphenylketene, di-Z rZ-butylketene [19824-34-17, and bis(trifluoromethyl)ketene, are quite stable as monomers. Ketenimines tend to polymerize. The dimerization of thioketenes results in 1,3-dithiacyclobutanones (6) (45), a type of dimer not observed with ketenes. 

The silylated lithium ynamine 192 is generated by metaUation with BuLi of 5 -methyl Af-phenyl-trimethylsilylethanimidothioate (190), via a ketenimine intermediate (191), as shown in equation 75. The interconversion between 191 and 192 can be discerned by silylation taking place at both the N- and -positions to afford the Af-silylynamide 193 and the bis(/ -silyl)ketenimine 194. In equation 76 are shown three possible synthetic... 

Thermal cycloadditions of ketenimines to cait>onyl compounds requires activation of the 0=0 bond. The highly electrophilic bis(trifluoromethyl) ketone reacts at high temperature with diphenyl-N-to-lylketenimine (equation 73). Lanthanide shift reagents such as tris(6,6,7,7,8,8,8-heptafIuoro-2,2-di-methyl-3,S-octanedionato)-europium or -ytterbium [Eu(fod)3 or Yt(fod)a] are efficient catalysts for the cycloaddition of ketenimines with aldehydes (equation 74). The use of chiral catalysts such as tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato)-europium or -ytterbium [Eu(hfc)3 or Yt(hfc)3] has been found to generate only moderate enantiomeric excesses (20-40%). ... 

Bis(imino) thietanes, 343, 344, are prepared by reaction of isonitriles with iminothiiranes or of ketenimines with p-tolylsulfonyl isothiocyanate. Reaction of phosphonium ketimine ylides, for example, 312, and related compounds with isothiocyanates also gives bis(imino) thietanes, for example, 345. " Treatment of arylsulfonyl isothiocyanates with trimethylacetoisonitrile yields tris(imino)-thietanes, for example, 341. ... 

The zirconocene bis(phosphine) complex, 57, also coordinates Ar N-C=CPh2 (Ar = >-MeC6H4) to yield the zirconocene ketenimine derivative (r]5-C5H5)2Zr(r]2-(C, j/V)-Ar N=C=CPh2)(PMe3) 61 with loss of phosphine (Scheme 9). Similar chemistry is observed upon reduction of (775-CsMe5)2ZrCl2 53 with LiBuc in the presence of the ketenimine.24 However, in the latter example the base-free ketenimine complex is isolated. 

Although no preparatively useful metal-catalyzed [3-F 2]-cycloaddition reactions involving ketenes have been developed due to the pronounced [2-F2]-cycloaddition reactivity of this substrate vide supra), ketene derivatives, e.g. ketenimines, are much less prone to undergo [2 + 2] cycloadditions, so that [3-1-2] cycloaddition can successfully compete. However, instead of the primarily expected 2,4-bis(methylene)pyrrolidines or a-methylene-d -pyrrolines, substituted pyrroles are formed whenever double-hond isomerization is possible. For example, such a reaction smoothly proceeds with the parent MCP (4) and iV-phenyldiphenylketenimine (19) which provides 2-(diphenylmethyl)-4-methyl-l-phenylpyrrole (20) in 96% yield. 

Reactions of triphenyl-2,2-bis(trifluoromethyI)vinylidenephosphorane, synthesized from a cyclic ylide-ketone adduct. 7 Cycloaddition reactions of triphenylphosphoranylideneketenc. 8 Synthesis of triphenylphosphoranylidene-ketenimines. 9... 

Ai7lmethylene-3-phenyl-2-isoxazolin-5-ones 36 I eact with A-phenacylpyridinium bromide in the presence of triethylamine to give stable betaines 37 <97LA441>. Flash-vacuum pyrolysis of the isoxazolinone 38 results in the ketenimine 39, together with the bis(imino)propadiene 40 <96MI1318>. 

Cycloadducts of aliphatic isocyanates and perfluoromethacryloyl fluoride [the isomer of bis(trifluoromethyl)keten] undergo a 1,3-fluoride shift during synthesis or on heating, giving oxazinones (177). Pyrolysis of the latter compounds gives bis(trifluoromethyl)ketenimines by elimination of carbon dioxide (see Vol. 2,... 

Larksarp and Alper used a palladium(II) catalyzed cyclocarbonylation reaction to generate a series of more complex and biologically relevant 4(3 0-Penicillium chrysogenum), have been shown to exhibit PTK inhibition and cholecystokinin inhibition as well as antimicrobial, anti-convulsant, anti-depressant and anti-inflammatory properties. Reaction of o-iodoaniline, a substituted ketenimine, and carbon monoxide with palladium(II) acetate and l,l -bis-diphenylphosphino-ferrocene (dppf) under thermal conditions gave the desired quinazolinone in near quantitative yield. In the same report, the authors showed that similar reactions could also be conducted with isocyanates and carbodiimides (not shown). 

To a solution of 0.8 g dimethyl A -[l-(2-azidophenyl)ethyl]dithiocarbonimidate (3 mmol) in 15 mL dry toluene, was added 3 mL 1 M trimethylphosphane in toluene (3 mmol), and the mixture was stirred at room temperature until the evolution of nitrogen ceased (15-30 min). Then, 0.40 g methyl phenyl ketene (3 mmol) was added, and the reaction mixture was stirred at room temperature until the ketenimine band 2000 cm was not observed by IR spectroscopy (3-4 h). Upon removal of the solvent under reduced pressure, the residue was purified by silica gel column chromatography using hexanes/EtOAc (4 1 v/v) as the eluent to afford 0.90 g frans-2,8-dimethyl-l,l-bis(methylthio)-2-phenyl-l,2-dihydroazeto[2,l-i ]quinazoline as colorless prisms (Et20), in a yield of 85%, m.p. 141-142°C. 

Yields are only moderate (20—49%) and the ketenimines are accompanied by resinous by-products. Alternative routes to bis(fluoroalkyi)ketenimines involve dehydrofluorination of 2Sf-imidoyl fluorides, or treatment of the dangerously toxic perfluoroisobutene with mixtures of primary and tertiary... 

A-Alkyl- and JV-aryl-bis(trifluoromethyl)ketenimines, (CFj)jC C NR, add active-hydrogen compounds such as primary amines across the C=C bond,... 

The formation of 1,3-oxathiolane with chloral and 1,3-dithio-lanes with cycloaliphatic thioketones occurs regioselectively to yield the sterically less hindered products. On the other hand, aromatic thioketones, e.g., thiobenzophenone or 9/ fluorene-9-thione, intercept 8 to give comparable amounts of both regio-isomeric adducts. Usually, stereoisomeric dipolarophiles such as fumaronitrile and maleonitrile as well as dimethyl fumarate and maleate form 18 in a stereoselective manner. However, in the case of extremely electron-poor dipolarophiles, e.g., dimethyl 1,2-dicyanofumarate or ( )-l,2-bis(trifluoromethyl)ethylene-l,2-dicarbonitrile, non-stereospecific formations of the corresponding tetrahydrothiophenes are described. i- s This result is interpreted in terms of a stepwise reaction mechanism with a zwitterion as the key intermediate. Alternatively, this intermediate can cyclize to form seven-membered ketenimines of type 20. With R = Cp3, this product can be isolated in a crystalline form, whereas in the case of R = CN, stable lactam 21 is obtained only after addition of water (eq 10). 

Iminoazetidines have been prepared by either the thermal dimerization of iV-methyIdiphenylketenimine (81) or the base-catalysed dimerization of bis (trifluoromethyl)ketenimine (82). 

Bis(amino)-thietans may be prepared in moderate yields by the action of isocyanides on iminothiirans or of isothiocyanates on ketenimines (Scheme 59). ... 

AMI studies of the 2 - - 2-cycloaddition of ketenimines with imines show that the reaction involves a stepwise mechanism via an intermediate and two transition states. A computational investigation of the thermal 2 - - 2-cycloaddition between imines and ketiminium cations finds that the reaction takes place via a stepwise mechanism.The reaction of benzyne with Schiff bases, diimines, yields l,4-bis(2-substituted acridin-10-yl)benzene via an initial double 2 - - 2-cycloaddition. 

Secondary aminoacetylenes, which readily tautomerize to ketenimines, have been isolated and characterized for the first time by pyrolysis of 4-methylene-isoxazol-5(4//)-ones and trapping the products at -196 °C e.g. Scheme 115). Bis-dialkylaminocyclopropenones, prepared from tetrachlorocyclopropene and dialkylamines, pyrolize smoothly at 525 °C to furnish bis-dialkylamino-... 

Sterically hindered thioketenes also react across C=S bond-containing substrates". For example, t-butyl(isopropyl)thioketene reacts with thiobenzophenone to give the [2+2] cycloadduct in 41 % yield. In the reaction of bis-trifluoromethylthioketene with sulfurdiimides an exchange reaction occurs, resulting in the formation of ketenimines in 20-48 % yields" ". ... 

The [2+2] cycloaddition reaction of isothiocyanates with ketenimines proceeds at room temperature across the C=S bond of the isothiocyanates and the C=C bond of the ketenimines to give 2,4-bis(imino)thietanes. However, only reactive isothiocyanates, such as arenesulfonyl isothiocyanates (48-54 % yield) or phenylcarbonyl isothiocyanate (44 % yield), undergo this reaction... 

Also, in the reaction of 4 with 2,3-bis(trifluoromethyl) fumaronitrile a mixture of the corresponding [3+2] cycloadduct and the cyclic ketenimine is obtained. In the reaction of 4 with electron deficient acetylenes, 2,5-dihydrothiophene derivatives 9 are obtained. 

Finnerty, J., Mitschke, U., and Wentrup, C., Linear Ketenimines. Variable structures of C,C-dicy-anoketenimines and C,C-bis-sulfonylketenimines, /. Org. Chem., 67, 1084, 2002. 

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