Cyclopentannulation reactions with organoiron reagents. facile construction of functionalized hydroazulenes

Article abstract of DOI:10.1021/ja00173a020

Troponeiron tricarbonyl, 2-methyltroponeiron tricarbonyl, and 4-methyltroponeiron tricarbonyl are converted to fluxional tropyliumiron tricarbonyl salts by treatment with either trimethylsilyl or di-n-butylboron triflate. These pentadienyliron cations react with (η¹-allyl) (η¹-propargyl)-, and (η¹-allenyl)Fp complexes [Fp = C₅H₅Fe(CO)₂] to give ketohydroazulene cycloadducts derived, in each reaction, from a single tautomeric tropylium cation. The further reaction of two such cycloadducts 14 and 22b with lithium dimethyl cuprate gave tricyclic ketones 25a and b, through a sequence depicted as involving initial formation of an anionic acyliron complex, followed by migratory insertion and an intramolecular aldol condensation.