Aza-di-ir -methane rearrangements

In nitrogen systems, all three arrangements are in principle possible, i.e. the 1-, 2- and 3-aza-di- ir-methane rearrangements. Only the first of them has recently been investigated, while examples of the 2-and 3-aza-di- ir-methane rearrangement appear still missing from the literature. 

The first aza-di-ir-methane rearrangement to be reported is illustrated in equation (26). The product of the reaction is the imine and not the aziridine the latter could have formed upon rupture of the alternative bond of the cyclopropyldicarbinyl diradical intermediate. In this regard, the aza-di-ir-methane resembles the 1-oxa case, wiA reestablishment of the imine bond. 

The l-aza-di-TT-methane rearrangement depends on the type of substitution of the nitrogen atom. For example, aza-di-ir-methane rearrangement occurs with aryl-substituted imines and with oxime acetates, but not with the oxime (23) or the nitrile (24). ... 

Specific imine derivatives of otherwise reluctant (see preceding section) 3,7-unsaturated aldehydes and ketones are again photochemically reactive and cyclize in high yields when irradiated in the presence of a triplet sensitizer, they undergo the aza-di-ir-methane rearrangement, typical examples of which are shown for (31) - (32) (R = alkyl or phenyl). ... 

Aryl derivatives (29) of 3,3-dimethyl-5,5-diphenyl-1-azapenta-1, 4-diene undergo aza-di-ir-methane rearrangement on... 

The acetophenone-sensitized aza-di-ir-methane rearrangement of a series of l-aryl-4,4-dimethyl-6,6-dinhenyl-2-azahexa-2,5-... 

The photochemistry of 1,4-unsaturated systems has been studied intensively over the last three decades, as it can be exemplified by reactions like the di-ir-methane rearrangement or the oxa-di-TT-methane rearrangement. In this context, Armesto and co-workers reported a novel l-aza-di-Tr-methane rearrangement of 1-substituted-1-aza-1,4-dienes promoted by DCA sensitization. Because of the... 

The hetera-substituted di-ir-methane rearrangement is currently an active area of investigation. So far, most examples have been reported for oxa and aza substitution. From the available data, it appears that the rearrangement is operative only when the heteroatom is in the 1-position. Replacement of the sfP carbon at the 2-position or the sp carbon at the 3-position by heteroatoms such as 0, N, S, Se, B, P, etc. entails systems which have not been investigated or which have proved incapable of giving di-ir-methane products. 

The l-aza-S-oxa-di-ir-methane rearrangement of (25) does not occur. Instead, cis-trans isomerization and photoelimination of methanol are observed for this oxime (equation 21) Finally, the l-oxa-4-aza-di-iT-methane rearrangement of compound (26) also did not take place. This substrate gave rise to the photo-induced l,S-benzoyl migration shown in equation (28). ... 

We believe that the rearrangements of the di-ir-methane type observed in the DCA-sensitized irradiations of 1-aza- and 2-aza-1,4-dienes are important because the di-ir-methane process has been considered until now a paradigm of reactions that take place in the excited-state manifold only. Our results show that rearrangements of this type can also occur in the ground states of radical-cation intermediates. This opens the possibility of promoting di-ir-methane-type rearrangements by alternative thermal means. 

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