| Abstract
| - A new synthetic sequence involving the use of Ireland−Claisen rearrangement of propargylicacetates to form the corresponding benzannulated enyne-allenes followed by Schmittel cyclizationto generate benzofulvene biradicals for radical cyclizations leading to polycyclic aromatic compoundswas established. Treatment of 9-fluorenone (8) with the lithium acetylide 9 followed by aceticanhydride produced the propargylic acetate 10. A sequence of reactions occurred after 10 wasconverted to the corresponding silyl ketene acetal 11. An initial Ireland−Claisen rearrangementproduced the benzannulated enyne-allene 12, which then underwent a Schmittel cyclization reactionto generate the benzofulvene biradical 13. A subsequent intramolecular radical−radical couplingthen produced the formal Diels−Alder adduct 14, which in turn underwent a prototropicrearrangement to give the silyl ester 15 and, after hydrolysis, the carboxylic acid 16 in 57% overallyield from 10 in a single operation. An intramolecular acylation reaction of 16 produced the ketone17. The carboxylic acids 24−26 were likewise prepared from the diaryl ketones 18−20, respectively.However, the intramolecular [2 + 2] cycloaddition reaction of the benzannulated enyne-allene 33having a tert-butyl group at the allenic terminus occurred preferentially, producing the 1H-cyclobut[a]indenyl acetic acid 35 as the predominant product.
|
