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Vinyl ketenimines

The vinyl ketenimines 128 react as azadienes in [4+2] cycloaddition reactions. For example, reaction with isocyanates gives the cycloadducts 129 (38-54 %), with diaryl sulfides the cycloadducts 130 (29-33 %) and with diphenylketene the cycloadducts 131 (47-53 %) 5. [Pg.357]

The vinyl ketenimines 132 react with ynamines at 0 °C by a [2+2] cycloaddition across the C=N bond to generate the allene 133, which undergoes electrocyclic ring closure to... [Pg.357]

The vinyl ketenimine CH2=CH(Me)0=C=NTs also reacts as a diene with tetracyano-ethylene (77 % yield), maleic anhydride (88 % yield), dimethyl acetylenedicarboxylate (40 % yield) and PhC=C(CN)2 (100 % yield). Also, the vinylketenimine 138 reacts with diethyl azodicarboxylate to give a 94 % yield of the cyloadduct 139 and with 4-phenyl-4/7-l,2,4-triazole-3,5-dione to give the cycloadduct 140 in 53 % yield . ... [Pg.358]

There is no unity of opinion in the literature concerning a classification, i.e, whether to call these transformations aza-Claisen or aza-Cope rearrangements. It is accepted that the term aza-Claisen should be reserved only for those processes in which a carbon atom in the allyl vinyl ether system has been replaced by nitrogen357. Three different types of aliphatic 3-aza-Cope reactions which were studied theoretically are the rearrangements of 3-aza-l,5-hexadienes (610, equation 262), 3-azonia-l,5-hexadienes (611, equation 263) and 3-aza-l,2,5-hexatrienes (612, equation 264) (the latter is a ketenimine rearrangement )357. [Pg.868]

N-Vinyl heterocumulenes represent a new, highly reactive 2-azadiene species, which react, in general, with electron-rich alkenes and alkynes. Accordingly, we think it is of interest to complement the utility of electron-poor 2-azadienes in [4 + 2] cycloadditions by showing some examples involving A-vinyl isocyanates, -isothiocyanates, -carbodiimides, and -ketenimines. [Pg.46]

Ketenes easily add water,alcohols, amines and thiols to give derivatives of phosphorylated carboxylic acids ( -7). Phosphorylated ketenes undergo reactions of cyclo"aadition to vinyl ethers,diazomethane,styrene, cyclopentadiene, etc. From phosphorylated ketenes other phosphorylated cumulenes can be obtained,for example allenes,isocyanates,ketenimines... [Pg.248]

The thermal decomposition of terminal vinyl azides was originally believed to give only nitriles or, in some cases, indoles. The presence of 3-monosubstituted 1-azirines, however, has been inferred in the photolytic decomposition of some terminal azides.22,29 30 The nitrile is thought to arise in a similar manner to the ketenimine by an analogous Curtius-type rearrangement. The ketenimine (53) derived from terminal azides is unstable and rearranges to the nitrile (54). [Pg.54]

Kurtz and Sheehter48 have observed similarly that irradiation of 3,4,5-triphenylisoxazole gives AT-phenylbenzoylphenylketenimine, 3-benzoyl-2,3-diphenyl-l-azirine, and 1,4,5-triphenyloxazole. The formation of the azirine and ketenimine from this reaction and from the decomposition of vinyl azides would suggest a similarity in mechanism. [Pg.61]

Monocyclic imino-ketenimines, in which the reactive functionalities are linked by an allylic or vinylic tether connecting the imino and ketenimino nitrogen atoms, undergo a formal intramolecular [2+2] cycloaddition to yield fused tricyclic 2-iminoazetidines, namely, azeto[l,2-a][l,3]thiazolo[4,5-rf] [pyrimidines 10 <02EJO4222>, and azeto[l,2-... [Pg.102]

Annelatlon reactions. The ketenimine 1 acts chemically as a vinyl phosphonate activated by the cumulated imino group and is useful as an annelation reagent for the synthesis of heterocyclic compounds. As such it condenses with the sodium salt of salicylaldehyde (2) to afford the benzopyrane in 3 in 52% yield. Similarly, the pyrrolizine 5 is available from the sodium salt of 2-formylpyrrole in 51% yield. ... [Pg.113]

A number of 2-iminothietanes have been prepared from ketenimines and thio-benzophenone ° or thioxanthone. Addition of carbon oxysulfide or carbon disulfide to the phosphonium ylide of a ketenimine 312 gives an imino- 3-dithiolactone as previously noted.Arylsulfonylisothiocyanates undergo cycloaddition at 50°C to vinyl ethers to give 2-iminosulfonylthietanes in 50-76% yields.A ( 2g -I- 2 ) process involving zwitterions was suggested on the basis of the observed stereochemistry. [Pg.564]

Although vinylnitrenes are not involved in the formation of 2ff-azirines from vinyl azides, such nitrenes must be invoked in order to explain the further reactions of the azirines (Scheme 2). Thermal or photochemical ring opening of the azirine to a nitrene, and subsequent 1,2-shifts explain the formation of ketenimines and benzyl cyanides. A competing electrocycliza-tion of the nitrene onto a phenyl substituent in the /(-position leads to the... [Pg.235]

Acyl sulfenes, like all sulfenes, prefer to participate as 2it components of [2 + 2] or [4 + 2] cycloadditions (Chapter 5). Nonetheless, a range of [4 + 2] cycloaddition reactions of acyl sulfenes have been described46,47 (Scheme 8-XII), including their 4n- participation in dimerization reactions46-48 and reactions with imines,49 carbodiimides,50 ketenimines,51 1-azirines,52 vinyl ethers,53 and ketenes.47 The reactions often provide mixtures of [4 + 2] and [2 + 2] cycloadducts, and the observed course of the reaction usually depends on the reaction conditions. Consequently, many of the observed [4 + 2] cycloadditions of acyl sulfenes proceed by a stepwise, polar addition-cyclization reaction. [Pg.301]

Also, the highly strained seven-membered ring ketenimine 29 adds the vinyl ether at room temperature to give the bicyclic adduct 30 in 81 % yield (two diastereoisomers, ratio 57 43)2. ... [Pg.342]

The vinyl aldehyde 112 also reacts with Ai-benzylmethylketenimine across the C=C bond of the ketenimine to give the unstable pyran derivative 113, which converts upon heating to give 114... [Pg.355]

In 1961, Smolinsky reported on vapor phase pyrolysis of a-azidostyrene (52, Scheme 5.8), which furnished 3-phenyl-2//-azirine as the main product and provided the first example of the synthesis of such strained heterocycles from vinyl azides. By analyzing the IR data of the pyrolysates produced from 52, it was shown one year later that N-phenylketenimine is formed as a side product. By utilizing IR and NMR spectroscopy at low temperature, Wentrup and coworkers have smdied recently the detailed structures of another azirine-ketenimine pair, generated by thermal or photochanical decomposition of an enazide. The transformation of vinyl azides into 2//-azirines is currently the most frequently used access to these heterocycles. The manifold chemistry of azirines was reviewed several times," " and most of the aspects of their synthesis from alkenyl azides are summarized in Chapter 6 (Gilchrist Alwes). Therefore, only some additional certain points are included here. [Pg.133]

Smolinsky and Pryde first observed azirine formation, together with small amount of ketenimin, by gas-phase pyrolysis of a-aryl substituted vinyl azides. [Pg.320]

The formation of 1-azirines (27) along with ketenimines (28) upon photolysis and thermolysis of vinyl azides was explained by the intermediacy of singlet vinylnitrenes ( 29). ° Ketenimins can serve as a precursor to nitriles (30) if R =H. [Pg.320]


See other pages where Vinyl ketenimines is mentioned: [Pg.114]    [Pg.114]    [Pg.469]    [Pg.34]    [Pg.452]    [Pg.89]    [Pg.89]    [Pg.277]    [Pg.452]    [Pg.244]    [Pg.108]    [Pg.244]    [Pg.255]    [Pg.55]    [Pg.850]   


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