A novel stereospecific alkenyl-alkenyl cross-coupling by a palladium- or nickel-catalyzed reaction of alkenylalanes with alkenyl halides

Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation–Pd-catalyzed cross-coupling

“…In addition to (2Z,4E)-dienoic esters, some (2Z,4E,6E)-and (2Z,4E,6Z)-trienoic esters have been prepared in ≥98% selectivity by a newly devised Pd-catalyzed alkenylation-SG olefination tandem process. As models for conjugated higher oligoenoic esters, all eight stereoisomers for ethyl trideca-2,4,6-trienoate (23)(24)(25)(26)(27)(28)(29)(30) have been prepared in ≥98% overall selectivity.…”

“…Despite highly selective and satisfactory results described above, our continued search for a more generally applicable and straightforward route to conjugated di-and oligoenes led to the discovery in 1976 of the Pd-catalyzed alkenyl-alkenyl coupling with alkenylalanes (27) and subsequently with alkenyl derivatives containing Zr (28) and Zn (29), collectively known as Negishi coupling (30,31). Along with the subsequently developed alkenylboron version (Suzuki coupling) (32)(33)(34), the Pd-catalyzed alkenylalkenyl coupling (35) has collectively begun establishing itself as the modern "cornerstone" of alkene and oligoene synthesis.…”

“…The ultimate goal of this and related studies in the authors' group is to be able to synthesize in high yields, efficiently, and selectively (≥98%) all possible types of conjugated di-, tri-, and higher oligoenes. In this study, however, attention is focused on the following three specific aspects: (i) synthesis of all possible stereoisomers of conjugated dienoic and trienoic esters containing (E)-and/or (Z)-1,2-disubstituted alkene units via alkyne elementometalation (36) -Pd-catalyzed cross-coupling of Negishi (Zn, Zr, Al) (27)(28)(29)(30)(31) and Suzuki (B) (32)(33)(34) versions, (ii) critical comparison of the Pd-catalyzed alkenylation routes with the carbonyl olefination routes represented here by mutually complementary HWE (14)(15)(16) and SG (14,17,18) olefinations as well as Heck alkenylation (37-39), all of which are known to proceed via π-addition-β-elimination and, (iii) feasibility of synergistic uses of Pd-catalyzed alkenylation and carbonyl olefination.…”

“…ii. Syntheses of the (2Z,4E) and (2E,4Z) isomers of some conjugated dienes by Negishi (27,35) and Suzuki (32,33,35,41) alkenylations are known. Whereas Negishi coupling has uniformly led to ≥97-98% stereoselectivity, Suzuki reported stereo scrambling to varying extents (≥5%) for the synthesis (18) and used in the subsequent Stille coupling for a total synthesis of (+)-sorangicin A (46).…”

Exploiting the C-H bond in metal catalyzed C-C bond forming reactions

“…Also the use of reagents in a catalytic fashion is highly attractive for increasing efficiency of synthetic reactions. Here, metal catalyzed cross-coupling reactions 2,3 have been very successful during the last decades, which were recognized by the Nobel Prize in chemistry 2010 for Akira Suzuki, 4,5 Ei-ichi Negishi,6,7 and Richard Heck 8 for their achievements in this field.…”