Diazirines properties

The diazirines are of special interest because of their isomerism with the aliphatic diazo compounds. The diazirines show considerable differences in their properties from the aliphatic diazo compounds, except in their explosive nature. The compounds 3-methyl-3-ethyl-diazirine and 3,3-diethyldiazirine prepared by Paulsen detonated on shock and on heating. Small quantities of 3,3-pentamethylenediazirine (68) can be distilled at normal pressures (bp 109°C). On overheating, explosion followed. 3-n-Propyldiazirine exploded on attempts to distil it a little above room temperature. 3-Methyldiazirine is stable as a gas, but on attempting to condense ca. 100 mg for vapor pressure measurements, it detonated with complete destruction of the apparatus." Diazirine (67) decomposed at once when a sample which had been condensed in dry ice was taken out of the cold trap. Work with the lower molecular weight diazirines in condensed phases should therefore be avoided. 

The properties of the diazirines and the analytical results showed that a new class of isomeric diazo compounds had been discovered. The three-membered ring structure (65), which is made probable by the synthetic methods, is confirmed by the reactions of the diazirines. 

The proof of the three-membered structure of the diazirines concludes the discussion on the three-membered ring structure of the aliphatic diazo compounds. The knowm linear aliphatic diazo compounds and the newly prepared cyclic diazo compounds (diazirines) are two independent classes of compounds completely different in their physical and chemical properties. An interconversion of the linear and cyclic diazo compounds has not so far been possible. 

It has been found that the catalytic activity of PKC is enhanced by a lipid component of the cell membrane, namely phosphatidylserine. This activity is further stimulated by sn-1,2-diacylglycerol. Oleic acid also activates the enzyme in the presence of 1,2-diacylglycerol, and thus it is presumed to mimic phosphatidylserine. In order to identify that modulating binding site for oleic acid on PKC, a photoaffinity analogue was devised. A carbene generating photophore, diazirine was placed in the apolar terminus of the unsaturated fatty acid ligand (30, Fig. 12). The synthesis and the photochemical activation properties were reported by Ruhmann and Wentrup [113]. 

Recently, a variety of authentic 1,2-diazacyclopropenes (sometimes called diazirines) have been prepared, and these have been found to have very different properties from the diazoalkanes. The simple 1,2-diazacyclopropenes are colorless and do not react with dilute acids, bases, or even bromine. The... 

The absorption properties of diazirines are characteristic. All possess an absorption band in the near ultraviolet (kmax 350 to 380 nm) which is resolved into a series of sharp peaks in non-polar solvents such as hexane. Extinction coefficients are modest, usually around 300 M-1 cm-1, but... 

In an attempt to reduce the size of the photoreactive group, Emi and Khorana (1980) investigated the properties of tetrafluorodialkyl diazirines. Unfortunately these compact molecules (Fig. 3.17) did not yield insertion products on photolysis, but rearranged internally by alkyl migration to give olefins, and underwent intramolecular insertion to yield cyclopropanes. 

Brunner et al. (1980) have reported on the properties of a new class of aryl diazirines, the 3-aryl-3-trifluoromethyldiazirines. Besides forming a class of the most attractive photoactivatable reagents available, these molecules may be made in far higher yield than the corresponding 3-H-diazirines. The route used, which incidentally fails with the 3-H-com-pounds (Smith and Knowles, 1975), is shown in Fig. 3.24. Two drawbacks are the large number of steps involved and the difficulty of preparing... 

It should be pointed out that despite their high reactivity carbenes are selective, and while they will react with hydrocarbons in the absence of nucleophiles, a nucleophilic group exposed within the bilayer will preferentially be attacked. Some properties of the three most thoroughly tested reagents iodonaphthyl azide, adamantane diazirine, and 3-trifluoromethyl-3-(m-iodophenyl)diazirine are summarized in Table 6.1. There follows a brief description of a typical experimental procedure, a discussion of control experiments, and several caveats, followed by some examples of the applications of hydrophobic reagents. 

Both [5-12SI]iodonaphthylazide (Karlish et al. 1977) and [3H]adaman-tane diazirine (Farley et al. 1980) labeled the a-subunit strongly and the (3-subunit hardly at all. The simplest interpretation of this result is that the (3-subunit is a peripheral protein, tightly attached to the a-subunit. The possibility remains, however, that the (3-subunit is relatively unreactive towards hydrophobic reagents even though the two used in these studies have quite different properties. A further possibility that must be taken into account when considering multisubunit membrane proteins is that (3 penetrates the bi layer but is shielded from the hydrocarbon phase by neighboring a-subunits. ... 

Diazirines are thermally unstable and generate a carbine radical intermediate. This property has been used with hydrazones as a route for forming cyclopropanes (2) as illustrated in Eq. 2 ... 

In the last decade, limited research has been published on the thermodynamic properties of diazirines and diaziridines. Extensive coverage of this topic was presented in CHEC-II(1996) <1996CHEC-II(1A)347>. 

Diazirines are a reliable source of carbenes, and this property has dominated their application in the last decade. In particular, there has been considerable use of diazirines in macromolecular systems, both chemical and biological, and this is the subject of a recent review <2005SFM178>. Synthetic applications are documented in Section 1.11.6. 

The protonated diaziridine is more easily reducible than the diazirine, which has too weakly basic properties to be protonated in aqueous solution. In alkaline medium in which both are unprotonated, the diazirine is the more easily reducible. This explains why it has been difficult to obtain good yields of diaziridine by chemical and catalytic reduction of a diazirine if such a reduction is to result in a high yield of diaziridine, it must be performed in an alkaline medium. 

In recent years, selective laser excitation and ultrasensitive fluorescence detection has been elegantly used to study isolated and single molecules, and Lu and Xie report that recent advances in near-field and far-field fluorescence microscopy now allow the imaging of single molecules and the recording of their fluorescence properties at room temperature. The exceptional photostability of 2-(2 -hydroxy-phenyl)perimidine has been discussed by Catalan et al. in relation to the fluorescence of the enol, and the reported value of 240 ps for the fluorescence lifetime of adamantyldiazirine represents the first such record for a diazirine (Buterbaugh et ai). Most phenanthrene derivatives do not usually exhibit... 

Aryl-1 -fluorocyclopropanes 2 were synthesized by irradiation of a 3-aryl-3-fluoro-3//-diazirine and an alkene (2 > 300 nm, 25 °C) in a screw-top Pyrex Carius tube (Houben-Weyl, Vol. E19b, p980). The starting 3-aryt-3-fluoro-3//-diazirines were prepared from the corresponding 3-aryl-3-bromo-3//-diazirines and anhydrous tetrabutylammonium fluoride. The products were purified by column chromatography on silica gel (purity > 97%). Due to the explosive properties of diazirines, this method is not suitable for large-scale preparations. 

The adducts 9 of arylchlorocarbenes, generated thermally or photolytically from the corresponding diazirines, to electrophilic alkenes have also been prepared the physical properties of these cyclopropanes were not reported. 

The diazirine method allows the electronic properties of organo(organooxy)carbenes to be characterized. 

Aryl(methoxy)carbenes, generated photolytically from 3-aryl-3-methoxy-3//-diazirines, underwent addition to 1,1-dimethylallene to give methylenecyclopropane derivatives 1 (no yields or physical properties of the products were reported). ... 

The diazirines are the best source of dialkoxycarbenes in practice side products are not formed on reaction with alkenes. However, their explosive properties and the decidedly nucleophilic character of the carbenes they generate, limits the diazirine route for the preparation of 1,1-dialkoxycyclopropanes. On the other hand, the diazirine method is ideal for physicochemical... 

The addition of arylfluorocarbenes, generated from the corresponding diazirines, to al-kenes has very often been used during physicochemical investigations.122 125- 128 For that purpose, a series of 1-fluoro-l-phenylcyclopropanes 3, from electron-rich and electron-poor alkenes, were synthesized, although yields or physical properties were not reported. 

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