An intramolecular Cannizzaro-type hydride transfer to an in situ prepared allene enables the synthesis of ortho-fused 4-substituted cycloocta-2,5-dien-1-ones with unprecedented technical ease for an eight-ring carboannulation. Various derivatives could be obtained from commercially available (hetero)aryl aldehydes, trimethylsilylacetylene, and simple propargyl chlorides in good yields.

(2016) Diversification of ortho-fused cycloocta-2,5-dien-1-one cores and 8 to 6-Ring conversion by sigma bond C-C cleavage. 22 (35 A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk

Substituted chrysenes have been swiftly synthesised by the 6-endo-dig cyclisation of ethynylnaphthalenes using platinum(II) chloride. Cyclisation precursors were directly prepared from commercially available 2-bromoaldehydes in a telescoped synthetic procedure involving a Cannizzaro triggered cascade and subsequent dehydration and desilylation. This short synthetic procedure allows rapid access to derivatives of biologically active molecules with useful electronic properties.

An intramolecular Cannizzaro-type hydride transfer to an in situ prepared allene enables the synthesis of orthofused 4-substituted cycloocta-2,5-dien-1-ones with unprecedented technical ease for an eight-ring carboannulation. Various derivatives could be obtained from commercially available (hetero)aryl aldehydes,t rimethylsilylacetylene,a nd simple propargyl chlorides in good yields.Readily(oftencommercially)available2-bromo(hetero)aryl aldehydes (1,S cheme 1) constitute powerful and popular units for the construction of ortho-fused carbocyclic rings. [1] Tw os trategies commonly employed in the multitudinous syntheses described in the literature involve 1) the derivatization of 1 to intermediates of type A,w ith a p-system attacking an electrophile that is ultimately derived from the aldehyde by functional-group manipulations (e.g., an alcohol, acetal, or even the aldehyde itself);o r2 )formyl group homologation to an anion-stabilizing unit that attacks as uitably activated p-bond (B). Whereas many elegant catalytic systems that use intermediates A or B have already been described, [2,3] thep reparation of the suitable precursors is often step-intensive,r aising questions on the overall process efficiency in the "age of sustainability".[4] We speculated that an ew annulation strategy,b ased on aC annizzaro-type reaction via intermediate C,might be possible.Asthe hydride transfer simultaneously exposes apowerful Michael acceptor (ynone or equivalent) and ac arbanion in close proximity, efficient annulation might be expected to occur (especially if C is directly attained in situ). Herein, we describe the use of such as trategy for the formation of eight-membered rings. Thep aucity of direct single-pot/step procedures to such medium rings attests to the known issues associated with their synthesis;[5] they therefore provide as tringent test for strategy C. Although redox-based Cannizzaro reactions, including asymmetric and triggered C À Cb ond-forming versions,h ave recently been developed, [6] to the best of our knowledge,they have not been employed for carboannulation reactions to medium rings.G enuine single-pot/step procedures to eight-membered rings are very limited-Reppes historical catalytic access to cyclooctatetraene [7] and Murakamis [4+ +2+ +2] approach [8] being notable exceptions.Modern alternatives frequently describe catalytic cyclizationst hat proceed with exquisitely high yields (for the final step). Unfortunately,t heir overall synthetic efficiency is often compromised by the multistep syntheses required to obtain the cyclization precursors.[9]

One-Pot Cannizzaro Cascade Synthesis of ortho-Fused Cycloocta-2,5-dien-1-ones from 2-Bromo(hetero)aryl Aldehydes. -Starting from 2-bromo(hetero)aryl aldehydes, diverse terminal acetylenes and 1-chloropropargyl(hetero)arenes an access to ortho-fused cycloocta-2,5-dien-1-ones is developed which tolerates various functional groups. -(BURROUGHS, L.; ECCLESHARE, L.; RITCHIE, J.; KULKARNI, O.; LYGO, B.; WOODWARD*, S.; LEWIS, W.; Angew. Chem., Int. Ed. 54 (2015) 36, 10648-10651, http://dx.