1.2- Diazabicyclo 6-heptenes

The fully saturated pyrazolidines have been utilized as models for the study of the nitrogen inversion of hydrazines. For instance, (75), a 2,3-diazabicyclo[2.2.1]heptene derivative, presents a consecutive inversion process at two nitrogen atoms with an activation barrier... 

Some 2,3-diazabicyclo[2.2.1]heptene derivatives, for example, 175, with an aryl iodide and allyltributyltin in the presence of [Pd(allyl)Cl]2 in toluene provide unexpected products 176. It is interesting to note that aryl iodide is recovered almost completely but no reaction can be observed in its absence. When the aryl iodide is replaced by a Lewis acid, good yields of 176 are obtained. The reaction is very slow in toluene, but in ionic liquid [bmim]PF6 the reaction rate is significantly enhanced (Equation 21) <2005SL2273>. 

Photochemical denitrogenation of the stereolabeled diazabicyclo[2.2.1]-heptene DBH-1 leads to both inverted and retained bicyclo[2.1.0]pentane (housane) products, and the effect of solvent viscosity in this reaction has been examined by Adam et... 

Steel and coworkers194 have also noted that 2,3-diazabicyclo[2.2.1]-heptene-2 (39) quenches the fluorescence of naphthalene. A more extensive study of this compound was carried out by Engel195 who reported that there was a sharp drop in the efficiency of sensitized decomposition and in the rate of sensitizer fluorescence quenching as the sensitizer singlet energy fell below that of 39. This points out a key difference between azo compounds and the cases discussed previously namely, there is a spectroscopic azo singlet state lying below that of the sensitizer. 

The ultraviolet absorption spectrum has an intense band with a maximum below 200 mg and a finely structured long-wavelength band from about 280 to 330 mg (e 308.5 mg = 176 liter/mole cm.). The long wavelength band remains diffuse under high resolution. The shape of this band is unusual, but appears to be a common feature of all the diazirines so far reported (see later) and is reminiscent of the absorption spectrum of 2,3-diazabicyclo[2,2,l]-2-heptene, another molecule containing a strained nitrogen double bond. ... 

Among the bicyclic systems rate parameters have been measured for the gas phase decomposition of 2,3-diazabicyclo[2,2,l]-2-heptene ... 

EMISSION YIELDS AND FLUORESCENCE LIFETIMES IN THE PHOTOLYSIS OF 2,3-diazabicyclo-[2.2.1]heptene-2 (BDH) and 2,3-diazabicyclo[2.2.2]octene-2... 

The stereochemistry of pyrazoline deazetizations is startling and, even now, difficult to understand. A case in point is the formation of bicyclo[2.1.0]pentane from 2,3-diazabicyclo[2.2.1]heptene. When the stereochemistry of the reaction is tested by introduction of labels at C(5) and C(6), it is found that product formation occurs with preferential inversion of configuration (Figure 49). Roth and Martin explained this in terms of backside displacement from a diazenyl biradicaP, but, as described above, the... 

Interestingly the inversion observed for 2,3-diazabicyclo[2.2.1]heptene is not found in the deazetization of its lower homologue, 2,3-diazabicyclo[2.1.1]hexene-5-exo-d which gives bicyclo[1.1.0]butane-2-d with a 1 1 exo endo distribution of the label. There is evidence, however, that the hydrocarbon product may be produced in a chemically activated form and so the final label distribution might be the result of secondary isomerization. ... 

The acid-catalyzed ring opening of 2,3-dibenzyloxycarbonyl-2,3-diazabicyclo[2.2.1]heptene 304 gives the bicyclic... 

A soln. of 2-acetyl-5-methyl-6-phenyl-2,3-dihydro-4H-l,2-diazepin-4-one in methanol exposed 3 hrs. to sunlight in a Pyrex flask -> 2-acetyl-5-methyl-6-phenyl-l,2-diazabicyclo[3.2.0]-6-hepten-4-one. Y 88%. F. e. s. J.-L. Derocque,W. J. Theuer, and J. A. Moore, J. Org. Chem. 33, 4381 (1968). 

What factors contribute to the more positive values for the cyclic compounds Using the data above and data from Chapters 1 and 3, estimate AH for decomposition of 2,3-diazabicyclo[2.2.1]heptene according to the equation below ... 

Dihydro-1,2-diazabicyclo [3.2.0] -3-hepten-6-ones MI-312 and XII-313 and diazepinones XII-314 are readily interconvertible ring systemsand all three can give l-amino-3-pyridinol salts (see Section IV.3., p. 839) or 3-pyridinols. When heated in methanol, the 2-acetyl- or 2-benzoyl-derivative of MI-313 rearranges to several products including 6-acetamido- or 6-benzamido-3-hydroxy-4-methjd-5-phenylpyridine (XII-317) in 17% and 68% yield, respectively, presumably through intermediates such as XII-315 and... 

Several simple 1,3-biradicals have been directly observed spectroscopically. Photolysis of 2,3-diazabicyclo[2.2.1 ]heptene in a frozen solvent at temperatures below 10 K produced a simple biradical, 1,3-cyclopentanediyl, the triplet state of which was directly observed by Closs using EPR spectroscopy (Eq. 11.85). Similarly, a series of substituted 1,3-cyclobutane-diyls was produced (Eq. 11.86), showing that substituent effects on simple, triplet biradicals mirror those of conventional free radicals. 

Eqs. 16.68-16.69 show prototype azoalkanes, also known as 1,2-diazenes, or just azo compounds. A primary use of cyclic diazenes has been to provide an alternative entry into biradical structures that have been postulated as intermediates in other thermal or photochemical reactions. For example, photolysis of 2,3-diazabicyclo[2.2.1]heptene produces 1,3-... 

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