Other diazirines as photoaffinity reagents

Just as we inquired for diazo compounds and azides, we may ask why certain diazirines are not used as photoaffinity reagents and what prospects there are for new diazirine reagents. 

Unsubstituted alkyl diazirines are ruled out because carbenes from them rearrange to olefins (Fig. 3.14). The constraints of the caged ring system do not allow this possibility with the useful adamantane diazirine, although here a fraction of the carbene is lost by intramolecular insertion (Fig. 3.15). 

Flaloaryldiazirines can be synthesized in high yields but they should not be used as photogenerated reagents because some of their reaction products may be labile (for example, Fig. 3.16). 

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. 

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