PALLADIUM-CATALYZED CROSS COUPLING INVOLVING PROXIMALLY HETEROFUNCTIONAL REAGENTS (PALLADIUM, CROSS-COUPLING)
Abstract
A number of Pd-catalyzed cross coupling reactions involving proximally heterofunctional organometallics and/or organic electrophiles have been studied. Those reagents that contain (alpha)-heterofunctional groups include (alpha)-silylorganometals, (alpha)-heteroarylmetals, (alpha)-metallovinyl ethers, (alpha)-metalloyinyl thioethers, (alpha)-heteroaryl halides, and acyl halides. Since (alpha)-heteroorganometallics containing alkali metals or Mg do not readily react with alkenyl or aryl electrophiles, and Pd catalysis provides an attractive solution to this general problem. Metal enolates, (beta)-heteroarylmetals, (beta)-halovinyl halides, and (beta)-haloallyl halides represent a synthetically interesting class of (beta)-heterofunctional reagents. Ketone enolates containing B undergo a remarkably facile and selective allylation catalyzed by Pd-phosphine complexes. The reaction promises to significantly expand the scope of the enolate alkylation. 1,4- And 1,5-dicarbonyl compounds suitable for annulation are readily and selectively obtained by using 2,3-dichloropropene and 1,3-dichloro-2-butene, respectively. The Pd-catalyzed reaction of chloroiodoethene with alkynylzincs provides the corresponding chloroenynes readily convertible into terminal diynes which, in turn, are vonvertible into unsymmetrical diynes. The Pd-catalyzed cross coupling reaction of (gamma)-heterosubstituted allylic electrophiles provides a synthetic equivalent to conjugate addition via allylation. With (alpha)-allylalkenylsilanes, a highly stereoselective and high yield method for the syntheses of (E)- or (Z)-(alpha)-alkylidenetetrahydrofurans and (E)- or (Z)-(gamma)-alkylidene-(gamma)-lactones has been developed. The synthesis of (E)-5-hexylidenedihydro-2(3H)-furanone represents the first stereoselective synthesis of an (E)-(gamma)-alkylidene-(gamma)-lactone.
Degree
Ph.D.
Subject Area
Organic chemistry
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