Free radical addition of isobutyric acid to α,ω-diolefins. A new route to α,α,α′,α′-tetramethylalkanedioic acids

Free-Radical Rearrangements

“…Cyclizations of the substituted 5-hexenyl radicals generated by homolytic additions to 1,6-dienes show the same features as those of the simpler systems discussed above: 1,5 ring closure is usually [see, however, Bradney et al (210)] preferred (191-193, 201-211a), and cis-disubstituted products frequently predominate over trans (192,211). However, substituents at the 2 and 5 positions hinder five-membered ring formation of the primary adduct, thus causing increased yields of acyclic and sixmembered cyclic products (198,(211)(212).…”

“…The former reaction gives good yields of five-membered cyclic products. Other examples of the behavior of substituted dienes include the copper-catalyzed reaction of benzoyl peroxide with geranyl acetate (213) and with 6-methylhepta-l,5-diene (214) and the addition of a vari ety of substituted radicals to 3,7-dimethylocta-l,6-diene (210). The other primary adduct (60), being a 4-pentenyl system, does not cyclize.…”

Highly Selective Synthesis of Polyfunctionalized Carbo- and Heterocycles Based on Ring Expansion of Squaric Acid Derivatives

“…Whereas the Baldwin rule predicts a disfavored process for 5-endo cyclization, 22 the 5-endo mode predominates even if the acyl radical has a radical acceptor [e.g., R=CH=CH 2 (as exemplified in Figure 5), Ph, C≡CPh in 39] to accommodate the advantageous 5-exo mode. 23 Analogously, some sporadic exceptions have been reported, for example, with 4-phenyl-4pentenyl radical and its 5-oxa analog 55 24 and with 2-formylbenzoyl radical 56 25 which cyclized to 3-phthalidyl radical 57 400 times faster than the 5-hexenyl radical cyclized to cyclopentylmethyl radical (Figure 5).…”

5-Endo-Trig Radical Cyclizations

“…The alkyl-substituted radical 20 gave cyclopentane 21 but in very low yield (3% based on 82% conversion of 1,5hexadiene, Scheme 8). 10…”