PALLADIUM-CATALYZED ALLYLATION OF ORGANOMETALS AND KETONE ENOLATES (HOMOGENEOUS, METAL, CATALYSIS)
Abstract
Reaction of organometallic reagents with allylic electrophiles is a synthetic methodology of potential importance. In the present work the effect of palladium-phosphine complex as catalyst in such reactions has been investigated. Three kinds of organometallics have been studied; namely, alkenylmetals, arylmetals, and metal enolates derived from ketones. Alkenylmetals derived from alkynes via either hydrometallation or carbometallation, undergo palladium-catalyzed cross-coupling with a wide variety of allylic electrophiles to produce 1,4-dienes with a high degree of regio- and stereocontrol. The scope of this reaction with respect to the nature of the leaving group of the allylic electrophile has been studied. The alkenyl-allyl coupling reaction has been carried out in an intramolecular fashion for the regioselective formation of five-membered carbocycles. Allylation of metal enolates, in particular the potassium enoxytriethylborates, derived from ketones has been studied in the presence of catalytic palladium-phosphine complex. Allylic halides, as well as, allylic acetates participate in such reaction to produce the (alpha)-monoallylated ketones in high yields. The reaction is highly regio- and stereospecific with respect to the structure of the allylic group, and is also remarkably regiospecific with respect to the enolate regiochemistry. The regiochemistry of the formation of the potassium enoxyborates from unsymmetrical ketones under both kinetically and thermodynamically controlled conditions has been studied using nuclear magnetic resonance spectroscopy. Palladium-catalyzed cross-coupling reaction of organozincs with acyl halides has been developed as a highly convenient route to ketones. Finally, a brief study has been carried out on the palladium-catalyzed cross-coupling reaction of alkenyl and arylmetals with (alpha),(beta)-unsaturated acetals and orthoesters. The products in these cases amount to the products of conjugate addition to the corresponding (alpha),(beta)-unsaturated carbonyl compounds.
Degree
Ph.D.
Subject Area
Organic chemistry
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