Linear Ketenimines. Variable Structures of C,C-Dicyanoketenimines and C,C-Bis-sulfonylketenimines

Abstract

C,C-dicyanoketenimines 10a-c were generated by flash vacuum thermolysis of ketene N,S-acetals 9a-c or by thermal or photochemical decomposition of alpha-azido-beta-cyanocinnamonitrile 11. In the latter reaction, 3,3-dicyano-2-phenyl-1-azirine 12 is also formed. IR spectroscopy of the keteniminines isolated in Ar matrixes or as neat films, NMR spectroscopy of 10c, and theoretical calculations (B3LYP/6-31G) demonstrate that these ketenimines have variable geometry, being essentially linear along the CCN-R framework in polar media (neat films and solution), but in the gas phase or Ar matrix they are bent, as is usual for ketenimines. Experiments and calculations agree that a single CN substituent as in 13 is not enough to enforce linearity, and sulfonyl groups are less effective that cyano groups in causing linearity. C,C-bis(methylsulfonyl)ketenimines 4-5 and a C-cyano-C-(methylsulfonyl)ketenimine 15 are not linear. The compound p-O2NC6H4N=C=C(COOMe)2 previously reported in the literature is probably somewhat linearized along the CCNR moiety. A computational survey (B3LYP/6-31G) of the inversion barrier at nitrogen indicates that electronegative C-substituents dramatically lower the barrier; this is also true of N-acyl substituents. Increasing polarity causes lower barriers. Although N-alkylbis(methylsulfonyl)ketenimines are not calculated to be linear, the barriers are so low that crystal lattice forces can induce planarity in N-methylbis(methylsulfonyl)ketenimine 3.

3-Pyridazinylnitrenes and 2-Pyrimidinylnitrenes

“…Azirenes are sometimes observed in the matrix photolysis of vinyl azides. 16 Furthermore, singlet (2-acyl)vinylnitrenes are found to cyclize to azirenes. 17 The The ring opening of 20 to 1-isocyanodiazopropene 23 also has a high calculated barrier, ca.…”

Synthesis and characterization of novel heterocycles based on tetrazine and hydrazonoyl halides

“…The starting reagents 1 [16], 12 [17], 15 [18], 16 [19], 20 [20], 21 [21], and 25 [22] were prepared as previously described. To a dry 100 mL round-bottom flask were charged 3,6-bisphenolyl-1,2,4,5-tetrazine (1) …”

“…The required 2-cyano-3-methylthio-3-phenylaminoacrylo nitrile 21 was prepared by the reaction of malononitrile with phenyl isothiocyanate in DMF in the presence of potassium hydroxide and the resulting thiolate was methylated with methyl iodide to give 2-cyano-3-methylthio-3-phenylamino acrylonitrile 21 [21]. Recently, the synthesis of bis-triazoles [27] from reactions of hydrazonoyl halides with ketene-N,Sacetal was reported.…”

“…The synthetic utility of nitrilimine cycloaddition reactions in the most cases deals with construction of low molecular weight five-membered heterocyclic ring systems [21]. The presented paper deals with the synthesis and investigations of new polymers which were prepared via 1,3-dipolar polycycloaddition of bis-hydrazonoyl dichlorides 26 and bismaleimide 27, two maleic protons (H1 and H2) can be assigned as multiplet at 4.24 and 5.19 ppm.…”

Preparation of 9-Substituted Pyridine-Stretched Adenines and Hypoxanthines

“…Calculated frontier orbital energies vary with configuration but variations in the values recorded in Table 1 do not change the conclusions. 2-(Bis-methylsulfanylmethylene)malononitrile 9 16 and 2-(methylsulfanyl-phenylaminomethylene) malononitrile 11 18 were prepared by literature methods.…”