Ketenimines 0=0 bonds

Ketenes and related compounds have been reviewed extensively (1 9). For the synthesis and synthetic uses of conjugated ketenes see Reference 10. Ketenes with three or more cumulated double bonds have been prepared (11,12). The best known is carbon suboxide [504-64-3] 3 2 preparative uses and has been reviewed (13—16). Thioketenes (17,18), ketenimines (19—21), and their dimers show interesting reactivity, but they have not achieved iadustrial importance to date. 

The 27T-electrons of the carbon-nitrogen double bond of 1-azirines can participate in thermal symmetry-allowed [4 + 2] cycloadditions with a variety of substrates such as cyclo-pentadienones, isobenzofurans, triazines and tetrazines 71AHC(13)45). Cycloadditions also occur with heterocumulenes such as ketenes, ketenimines, isocyanates and carbon disulfide. It is also possible for the 27r-electrons of 1-azirines to participate in ene reactions 73HCA1351). 

Using standard references and protocol, we find the three reactions are respectively endothermic by ca 2, 8 and 6 kJmol-1, or ca 2, 4 and 3 kJmol-1 once one remembers to divide by 2 the last two numbers because the allene is dialkylated. So doing, from equations 10 and 11 we find an average ca 3 kJmol-1 (per alkyl group) lessened stability for alkylated allenes than the correspondingly alkylated alkenes. This is a small difference that fits most naturally in the study of substituted cumulenes such as ketenes and ketenimines, i.e. not in this chapter. But it is also a guideline for the understanding of polyenes with more cumulated double bonds. 

The (aziridin-l-ylimino)phosphoranes (57) react with ketens to give nitrile derivatives, presumably from an intermediate ketenimine by breaking the N—N bond and migration of the aziridinyl group.60 They also react with acyl halides and... 

The homolysis of AIBN occurs in a concerted process with simultaneous breakage of the two C— N bonds to yield nitrogen and 2-cyano-2-propyl radicals. Reaction of the radicals with each other can occur in two ways to yield tetramethylsuccinodinitrile and dimethyl-A-(2-cyano-2-isopropyl)ketenimine ... 

The thermally induced cyclization of A -(benzyloxycarbonyl)phenyl ketenimines 415, obtained in a two-step, one-pot procedure from benzyl 2-azidobenzoates 414, led to 2-substituted-4/f-3,l-benzoxazin-4-ones 416 (Scheme 79). The reaction involves the formation of a new carbon-oxygen bond and migration of the benzyl group from the oxygen atom to the terminal carbon atom of the ketenimine fragment <2005S2426>. 

The effect of Coulombic repulsion described for ketenimine 18a can also be used to rationalize the higher energy of nitrene 16a relative to 16b, as well as the higher energy of azirine 17a compared to 17a and 17b. It is possible that the changes in relative orientation of the C=N and C—F bond dipoles that occur for 16a 17a and 17a -> 18a are at least partly responsible for the fact that this process is predicted to be substantially more endothermic (in the case of 16a 17a) or less exothermic (in the case of 17a 18a) than the... 

Some examples dealing with the [4 + 2] cycloaddition of ketenimines have been recorded (Scheme 58). Thus, thioketones and ynamines reacted with N-aryl ketenimines 257 through the carbon—nitrogen and the conjugated aromatic carbon—carbon double bonds to yield benzothiazine derivatives 258 (80JOC3766 82JOC3998) and substituted quinolines 259 (73JA5417), respectively. Simple ketenimines 261 were formed by reaction... 

Ketenimines with cis arylazo compounds give iminodiazetidines by addition across the carbon-carbon double bond (67JHC155,72JHC555,74JHC409). 

In the reaction of /h/f-difluoro ketones with amines, a,/I-unsaturated / -amino ketones are formed, either by inline formation and imine enaminc tautomerization or via elimination of hydrogen fluoride and subsequent substitution of the other fluorine.22 Geminal sp2-bonded difluoridcs arc converted into ketenimines.12-49,89,90... 

Ketenes are oxo compounds with cumulated carbonyl and carbon—carbon double bonds of the general structure R R C—C—O, where R1 and R2 may be any combination of hydrogen, alkyl, aryl, acyl, halogen, and many other functional groups. Ketenes with R1 = H,R2 H are sometimes called aldoketenes, those with R R- H, ketoketenes. The S— and N— analogues of ketenes are called thioketenes (R1R2C—C—S) and ketenimines (R1R C—C—NR), respectively. 

Diazoalkane adds to carbodiimides and ketenimines, preferentially to the carbon-nitrogen double bond of the latter, but the triazoline undergoes spontaneous isomerization to the triazole.367-371 The only exception is the addition of ethyl diazoacetate to benzoyl isocyanate where an isolable... 

C-H bond dissociation energies, 1, 298 C-N triple bond additions, 10, 427 C02, ketene, ketenimine complexes, 5, 84 CO and CNR reductive coupling, 5, 66 cyclopentadienyl alkyl and aryls, 5, 66 cyclopentadienyl carbonyl complexes, 5, 64 cyclopentadienyl hydrides, 5, 69 cyclopentadienyl isocyanide complexes, 5, 65 rf-acyl and rj2-iminoacyl complexes, 5, 82 fj3-complexes, 5, 87... 

Few 7r-bonded imine complexes have been prepared and investigated structurally. The only complexes of nonbridging 7r-bonded C=N investigated structurally are a substituted ketenimine complex (XLIV), an iminium complex (XLV), and a complex of the azine [(CF3)2C=N—)2 (XLVI) (see Table I). 

The ketenimine complex is unusual in that angle y for the complex is 11.9(10)° and the average S is 174°. These angles are indicative of a coordinated triple bond, rather than the expected double bond. This seemingly anomalous result can be rationalized on the basis of a large contribution of resonance form B to the structure of the ketenimine. This... 

Aza-, oxa-, and thiastanniranes containing exocyclic double bonds were prepared by the approach in Equation (57), using ketenes, ketenimines, thioketenes, and the stannylene [2,4,6-(CF3)3C6H2]2Sn . Yields were below 50%, but this appears to be a remarkably general route to heterostanniranes <1997JFC29>. 

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