Thiyl radical induced cyclizations of dienes. Cyclization of .alpha.-acoradiene, .alpha.-bulnesene, and geranyl acetate to cedrane, patchulane, and cyclogeranyl acetate products

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).…”

“…Preferential formation of the latter would be expected (4) since the transition state for trans cyclization (40) is less subject to nonbonded interactions than that for eis cyclization (41). Other substituted radicals behave similarly (191,192). Other substituted radicals behave similarly (191,192).…”

“…A good example of the effect of substituents is provided by comparison of the reactions of 58 and 59 with ethanethiol (192). The former reaction gives good yields of five-membered cyclic products.…”

Thiophenol‐Mediated 1,5‐Hydrogen Atom Abstraction: Easy Access to Mono‐ and Bicyclic Compounds

“…Similar results are obtained with translocated radicals stabilized by delocalization (products 3e, 3f and 3a). The relative configurations of the major isomers of 3a and 3b -3f have not been assigned, however, related systems possessing gem-diester substituents are known to give the cis-cyclopentanes as major isomers when R 1 ¼ CO 2 R or alkyl and R 2 ¼ H, and the trans-isomer when R 1 ¼ OTBDMS or phenyl and R 2 ¼ H. [5,28,29] Interestingly, the formation of non-substituted alkyl radicals is also possible. For instance, the tertiary alkyl radical derived from 1g affords the cyclic compound 3g in 83% yield.…”

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates

“…25, x FOR PEER REVIEW 24 of 4230). This account details some of the previously discussed selectivity for radical addition to electron deficient alkenes, and the key advancement of this work is the generation of 5-membered lactams with alkyloxyamino moieties 200, which is the result of preferential addition of an α-carbonyl radical to the oxime ether 199.…”