Radicals Claisen

Claisen rearrangement, 1194-1195 dehydration, 622 elimination reactions, 393 oxidation, 625-626 radical reactions, 243-244 characteristics of, 162-164 comparison with laboratory reactions, 162-164 conventions for writing, 162. 190 energy diagram of, 161 reduction, 723-725 reductive animation, 932 substitution reactions, 381-383 Biological reduction, NADH and, 610-611... 

The UV irradiation of the 2-allyloxy-4,5-diphenyloxazole 41 results in the predominant formation of 5-substituted-2(5/T)-oxazolones 44, in contrast to the thermal aza-Claisen rearrangement which readily affords the 2(3/T)-oxazolones 42. The photolysis proceeds via allyl-O bond scission with the generation of a radical pair that subsequently recombines to produce 5-substituted-2(5/T)-oxazolones. Similar results were obtained with 2-(benzyloxy)-4,5-diphenyloxazole (Fig. 5.75). °... 

Irradiation of the a-cyclodextrin complexes of m-alkoxyphenyl allyl ethers (35) gave only a single ortho isomer in each case, although in solution each ether gave two ortho and one para isomers via photo-Claisen rearrangements (Schemes 17 and 18) [156,157], This can be attributed to the difference in free volume available within the cavity near the two ortho centers and to the difference in accessibility of the radical fragments to them. In support of this conclusion, irradiation of the /1-cyclodextrin complexes of 35 results in no... 

To avoid the formation of ketenes by alkoxide elimination, ester enolates are often prepared at low temperatures. If unreactive alkyl halides are used, the addition of BU4NI to the reaction mixture can be beneficial [134]. Examples of the radical-mediated a-alkylation of support-bound a-haloesters are given in Table 5.4. Further methods for C-alkylating esters on insoluble supports include the Ireland-Claisen rearrangement of O-allyl ketene acetals (Entry 6, Table 13.16). Malonic esters and similar strongly C,H-acidic compounds have been C-alkylated with Merrifield resin [237,238]. 

Durand-Reville, T., Gobbi, L.B., Gray, B.L., Ley, S.V. and Scott, J.S., Highly selective entry to the azadirachtin skeleton via a Claisen rearrangement/radical cyclization sequence, Org. Lett., 2002, 4, 3847. 

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