The Effect of Configuration of Certain Unsaturated 1,4-Diketones on Addition-Cyclization Reactivity

HYDRIDE REDUCTIONS OF THE CIS AND TRANS-DIBENZOYLSTILBENES1

“…It is believed however that the zinc-acetic acid reductions proceed via competing 1,4-and 1,6-reactions and involve electron transfer, that the relative ease of reduction there depends upon the relative degrees of planarity of semiquinone-like intermediates, and that the different ratio of the resulting saturated diketone and furan is determined by the nature of the intermediate enolates involved. The reduction-furanizations of m-dibenzoylstilbene by the hydride reagents and by aluminum isopropoxide evidently involve a quite different mechanism and resemble more the acid-catalyzed nucleophilic additionfuranizations which occur particularly readily with other cis unsaturated 1,4diketones of this type (8).…”