Isomerization of diene

Deprotection can be effected at 25° in 90-95% yield by cleavage with the FeCl,/ AC2O system in ether as the solvent. Under these conditions no isomerization of diene or enyne units is observed. After cleavage, addition of Na2HP04 converts the FeCl, to insoluble FePO . 

Another possibility is based on a model of active sites proposed by Hubaut et al. (138), which derives from a previous investigation by the same group (139) (Fig. 40). In this model, the reactions involved in hydro-treating on Mo/Al catalysts are associated with the CUS configuration. Hydrogenation of aromatic compounds (toluene, pyridine, etc.) and isomerization of dienes require a or site, whereas sites... 

The discussion of cis-trans photoisomerization of alkenes, styrene, stilbene, and dienes has served to introduce some important ideas about the interpretation of photochemical reactions. We see that thermal barriers are usually low, so that reactions are very fast. Because excited states are open-shell species, they present new kinds of structures, such as the twisted and pyramidalized CIs that are associated with both isomerization and rearrangement of alkenes. However, we will also see familiar structural units as we continue our discussion of photochemical reactions. Thus the triplet diradical involved in photosensitized isomerization of dienes is not an unanticipated species, given what we have learned about the stabilization of allylic radicals. 

IS. Conformational Isomerism of Diene Systems Table 19. Computed relative energies of the conformers of 1,3-butadiene... 

Several types of photochemical valence isomerizations of dienes are known. The reactions shown in Eqs. (82)-(87) are typical. They represent... 

Liaw, B., Orchard, W., and Kutal, C., Role of the triplet state of (arylphosphine)copper(l) complexes in the photosensitized isomerization of dienes, Inorg. Chem., 27, 1311-1316,1988. 

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