Diversification of ortho ‐Fused Cycloocta‐2,5‐dien‐1‐one Cores and Eight‐ to Six‐Ring Conversion by σ Bond C−C Cleavage

Sequential treatment of 2‐C 6 H 4 Br(CHO) with LiC≡CR 1 (R 1 =SiMe 3 , t Bu), n BuLi, CuBr⋅SMe 2 and HC≡CCHClR 2 [R 2 =Ph, 4‐CF 3 Ph, 3‐CNPh, 4‐(MeO 2 C)Ph] at −50 °C leads to formation of an intermediate carbanion ( Z )‐1,2‐C 6 H 4 {C A (=O)C≡C B R 1 }{CH=CH(CH − )R 2 } ( 4 ). Low temperatures (−50 °C) favour attack at C B leading to kinetic formation of 6,8‐bicycles containing non‐classical C ‐carbanion enolates ( 5 ). Higher temperatures (−10 °C to ambient) and electron‐deficient R 2 favour retro σ‐bond C−C cleavage regenerating 4 , which subsequently closes on C A providing 6,6‐bicyclic alkoxides ( 6 ). Computational modelling (CBS‐QB3) indicated that both pathways are viable and of similar energies. Reaction of 6 with H + gave 1,2‐dihydronaphthalen‐1‐ols, or under dehydrating conditions, 2‐aryl‐1‐alkynylnaphthlenes. Enolates 5 react in situ with: H 2 O, D 2 O, I 2 , allylbromide, S 2 Me 2 , CO 2 and lead to the expected C ‐E derivatives (E=H, D, I, allyl, SMe, CO 2 H) in 49–64 % yield directly from intermediate 5 . The parents (E=H; R 1 =SiMe 3 , t Bu; R 2 =Ph) are versatile starting materials for NaBH 4 and Grignard C=O additions, desilylation (when R 1 =SiMe) and oxime formation. The latter allows formation of 6,9‐bicyclics via Beckmann rearrangement. The 6,8‐ring iodides are suitable Suzuki precursors for Pd‐catalysed C−C coupling (81–87 %), whereas the carboxylic acids readily form amides under T3P® conditions (71–95 %).