Griffin fragmentation

The benzo version of the cyclopropyl- ir-methane rearrangement has been reported for substrate (16). The products are shown in equation (19), of which cyclobutane (17) corresponds to the cyclopropyl- n-methane product. The two alkenes are secondary products from the cyclobutane, while the last two products derive from photocycloreversion of the starting material (Griffin fragmentation), the diphenylcarbene being trapped by the solvent (BuKDH) in the form of the ether. 

The 3-oxa-di- i -methane rearrangement is far less common. As a symmetrical system, the product should be a vinyl epoxide (equation 23). So far, no 3-oxa-di-T -methane products have been observed from the divinyl ethers depicted in the equation. It was shown that the solution photochemistry of (21a) derives from its singlet i , i -state and parallels that of the unsubstituted divinyl ether (21d) and of furan in the gas phase. All products could be rationalized in terms of the initial formation of a singlet vinyl-vi-nyloxy radical pair (equation 24). Triplet sensitization brings about cis-trans isomerization and consequent deactivation. Had the 3-oxa-di- ir-methane product, i.e. the vinyloxirane (22), been formed, it would have decomposed via Griffin fragmentation as confirmed by irradiation of an authentic sample. 

Pyrolysis, photolysis, and electronolysis of ethylene oxide (128) yielded similar products (P. Brown et al., 1966). Electron impact-induced fragmentation (129) of the epoxide (51) (P. Brown et al., 1966) was similar to the photochemical behaviour (130) of the epoxide (52) (Kristinsson and Griffin, 1966). Rearrangement of the a,/3-epoxy-ketone to the diketone after ionization (131) has been suggested to account for... 

The RR method has been used to characterize the structures of fragments of amyloid [40, 41]. Griffin et al. [40] have synthesized the j8-amyloid fragment (HzN-Leu-Met-Val-Gly-Gly-Val-Val-Ile-Ala-COaH) which is the C-ter-minus of the )8-amyloid protein. The structure of this molecule was... 

In contrast to the above findings, irradiation of 2-phenyl-1-azaspiro[2.2]pent-l-ene (243) in methanol resulted in a Griffin-type fragmentation and produced ethylene and 2-phenylazirinylidene (244). Three-membered rings are known to undergo [3- 2- -l] cycloelimination on irradiation.For example, cyclopropane has been photolyzed in the vapor phase and gives methylene and ethylene,while photolysis of ben-... 

Figure 6 Fragments of the peptide 34-42 showing the cis and trans conformations. Also indicated is the orientation of the carbonyl carbon chemical shielding tensor, with perpendicular to the plane. Note the different orientations of the C-C inter-nuclear vector with respect to the CS tensor components. Reprinted with permission of the American Chemical Society from Costa PR, Kocisko DA, Sun BQ, Lansbury PT Jr and Griffin RG (1997) Journal of the American Chemical Society, 119 10487-10493)...

---