Zinc enolates derived from substituted 1-aryl-2,2-dibromoalkanones reacted with 2-acyl-3H-benzo-[f]chromen-3-ones to give 1-alkyl-1-aroyl-1a-acyl-1a,9c-dihydro-1H-3-oxacyclopropa[c]phenanthren-2-ones which were formed as a single stereoisomer. Reactions of the same zinc enolates with 6-bromo-2-oxochromene-3-carboxamides (piperidides and morpholides) afforded 1-aroyl-6-bromo-1-alkyl-1a-piperidino-(morpholino)carbonyl-1a,7b-dihydrocyclopropa[c]chromen-2-ones with high stereoselectivity. Likewise,Reactions of 3-acyl-2H-1-benzopyran-2-ones with phenacyl bromide in the presence of bases were reported to give cyclopropane derivatives [1]. In continuation of our studies on cyclopropanation of heterocyclic compounds [2], in the present work we examined reactions of 2-acyl-3H-benzo[f]chromen-3-ones IIIa-IIIc with bromine-containing zinc enolates IIa, IIb, IId, and IIf, which were prepared from 1-aryl-2,2-dibromoalkanones Ia, Ib, Id, and If and zinc. The results showed that nucleophilic zinc enolates are capable of adding at the C 4 atom of the heteroring in spite of steric hindrances created by the fused benzene ring. Intermediates IVa-IVg thus formed undergo spontaneous intramolecular cyclization to 1-alkyl-1-aroyl-1a-acyl-1a,9c-dihydro-1H-3-oxacyclopropa[c]phenanthren-2-ones Va-Vg (Scheme 1, I, II, R 1 = Me, Ar = Ph (a), 4-MeC 6 H 4 (b), 4-EtC 6 H 4 (c), 4-BrC 6 H 4 (d); R 1 = Et, Ar = Ph (e), 4-ClC 6 H 4 (f); III, R 2 = Me (a), Ph (b), 2-furyl (c); IV, V, R 1 = R 2 = Me, Ar = 4-MeC 6 H 4 (a), 4-BrC 6 H 4 (b); R 1 = Me, R 2 = Ar = Ph (c); Ar = 4-MeC 6 H 4 (d); R 1 = Et, R 2 = Ph, Ar = ClC 6 H 4 (e); R 1 = Me, R 2 = 2-furyl, Ar = Ph (f), 4-MeC 6 H 4 (g). Scheme 1.
