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2005
Benzopyran derivatives
R 0350
Reactions of Zinc Enolates Derived from 1-Aryl-2,2-di-bromoalkanones with
6-Bromo-2-oxochromene-3-carboxamides,
16- 122 2-Acyl-3H-benzo[f]chromen-3-ones,
and 3-Oxo-3H-benzo[f]chromene-2-carboxamides. — Nucleophilic zinc enolates
are capable of adding at the C-4 atom of benzochromenones (II) in spite of steric hindrance caused by the fused benzene ring. The intermediates formed undergo spontaneous intramolecular cyclization to oxacyclopropaphenanthrenones (III). The reactivity
of the zinc enolates towards compounds having an amide-activated double bond, (V),
is also investigated. These reactions proceed with high stereoselectivity. Likewise, benzochromenecarboxylic acid morpholide (VII) reacts with the enolate derived from
(IVc) to the ring-closure product (VIII). The presence of the fused benzene ring in (VII)
does not hamper its reaction with the zinc enolate. — (SHCHEPIN, V. V.;
KALYUZHNYI, M. M.; SILAICHEV, P. S.; RUSSKIKH, N. Y.; SHCHEPIN, R. V.;
EZHIKOVA, M. A.; KODESS, M. I.; Russ. J. Org. Chem. 40 (2004) 9, 1353-1358;
Dep. Chem., Perm State Univ., Perm 614990, Russia; Eng.) — H. Hoennerscheid
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