Diversification of ortho-fused cycloocta-2,5-dien-1-one cores and 8 to 6-Ring conversion by sigma bond C-C cleavage

Eccleshare, Lee and Lozada-Rodriguez, Leticia and Cooper, Phillippa and Burroughs, Laurence and Ritchie, John and Lewis, William and Woodward, Simon (2016) Diversification of ortho-fused cycloocta-2,5-dien-1-one cores and 8 to 6-Ring conversion by sigma bond C-C cleavage. Chemistry - a European Journal, 22 . ISSN 1521-3765 (In Press)

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Abstract

Sequential treatment of 2-C6H4Br(CHO) with LiC≡CR1 (R1 = SiMe3, tBu), nBuLi, CuBr∙SMe2 and HC≡CCHClR2 [R2 = Ph, 4-CF3Ph, 3-CNPh, 4-(MeO2C)Ph] at -50 oC leads to formation of an intermediate carbanion (Z)-1,2-C6H4{CA(=O)C≡CBR1}{CH=CH(CH–)R2} (4). Low temperatures (-50 oC) favour attack at CB leading to kinetic formation of 6,8-bicycles containing non-classical C-carbanion enolates (5). Higher temperatures ( 10 oC to ambient) and electron deficient R2 favour retro σ-bond C-C cleavage regenerating 4 which subsequently closes on CA providing 6,6-bicyclic alkoxides (6). Computational modelling (CBS-QB3) indicates both pathways are viable and of similar energies. Reaction of 6 with H+ affords 1,2-dihydronaphthalen-1-ols, or under dehydrating conditions, 2-aryl-1-alkynylnaphthlenes. Enolates 5 react in situ with: H2O, D2O, I2, allylbromide, S2Me2, CO2 and lead to the expected C-E derivatives (E = H, D, I, allyl, SMe, CO2H) in 49-64% yield directly from intermediate 5. The parents (E = H; R1 = SiMe3, tBu; R2 = Ph) are versatile starting materials for NaBH4 and Grignard C=O additions, desilylation (when R1 = 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%); while the carboxylic acids readily form amides under T3P® conditions (71-95%).

Item Type: Article
Additional Information: This is the peer reviewed version of the following article: L. Eccleshare, L. Lozada-Rodriguez, P. Cooper, L. Burroughs, J. Ritchie, W. Lewis, S. Woodward: Diversification of ortho-fused cycloocta-2,5-dien-1-one cores and 8 to 6-Ring conversion by sigma bond C-C cleavage, Chem. Eur. J. 2016, xx, xxxx which has been published in final form at http://dx.doi.org/10.1002/chem.201601970. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Keywords: Annulation, Medium-ring compounds, Synthetic methods, Ring expansion, C-C activation
Schools/Departments: University of Nottingham UK Campus > Faculty of Science > School of Chemistry
Identification Number: https://doi.org/10.1002/chem.201601970
Depositing User: Bramwell, Roseanna
Date Deposited: 05 Jul 2016 13:30
Last Modified: 19 Sep 2016 22:09
URI: http://eprints.nottingham.ac.uk/id/eprint/34641

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