Aryl-alkenyl coupling

A. Aryl-Aryl, Aryl-Alkenyl and Alkenyl-Aryl Coupling Reactions. 483... 

Some of the notable recent developments in the Pd- or Ni-catalyzed aryl-alkenyl and alkenyl-aryl coupling reactions include the use of aryl and alkenyl chlorides along the lines of earlier discussions. lust a couple of representative examples of the aryl-alkenyl coupling reaction with alkenyl chlorides are shown in Scheme 33. 

The Pd-catalyzed aryl-alkenyl and alkenyl-aryl coupling reactions involving Zn, A1 and Zr have been applied to the syntheses of a fair number of natural products26. Recent examples published in the last several years include the syntheses of UB-165107 and (—)-diazonamide A108 (Scheme 35). 

SCHEME 35. Recent syntheses of natural products via Pd-catalyzed aryl-alkenyl or alkenyl-aryl coupling... 

Regeneration of tin hydride from the corresponding halide in situ by poly-(methylhydro)siloxane enables alkenyl-alkenyl- or alkenyl-aryl coupling by the use of only catalytic amount of tin (Scheme 74) [279-287]. 

Mechanism The Pd- or Ni-catalyzed alkenyl-alkenyl and alkenyl-aryl coupling reactions may proceed according to Scheme 5.25, involving the oxidative addition, transmetallation and reductive elimination. 

Subsequent studies have shown that alkenylzirconium derivatives generated in situ by hydrozirconation [46] of alkynes also undergo Pd- or Ni-catalyzed cross-coupling. As observed with alkenylalanes, Ni catalysts are generally satisfactory in the cases of alkenyl-aryl coupling [47] (Scheme 1-12), whereas Pd catalysts are more selective and distinctly superior to Ni catalysts in alkenyl-alkenyl and alkenyl-alkynyl coupling [48] (Scheme 1-13). 

Negishi, E., Baba, S. Novel stereoselective alkenyl-aryl coupling via nickel-catalyzed reaction of alkenylalanes with aryl halides. J. Chem. Soc., Chem, Commun, 1976, 596-597. 

Scheme 5.4.16 Alkenyl-aryl coupling in the synthesis of ent-thallusin...

Alkenyl-Aryl coupling. tran. -Alk enylalanes can be activated for coupling with aryl bromides or iodides with this nickel(0) complex to form arylated tran.r-alkenes in 65-957 yield (equation 1). Pd[P(C0H5)3]4 is a less effective catalyst. ... 

Alkenylboron derivatives are readily available by stereo-defined hydroboration of alkynes and used for the preparation of styrene derivatives by alkenyl-aryl coupling. Vinylboronic acid (81), the most simple alkenylboronic acid, is difficult to handle, because it undergoes uncontrollable polymerization. Its anhydride, 2,4,6-trivinylcyclotriboroxane (82)-pyridine complex, is stable, and can be used conveniently for the coupling. Vinylation of 2-bromoanisole with 82 proceeds in refluxing DME using K2CO3 as a base fo provide 2-vinylanisole (83) [80]. 

The synthesis of alkene-substituted arenes by cross-coupling can, in principle, be achieved either by the reaction of alkenyhnetals with aryl halides and related electrophiles or by that of arylmetals with alkenyl electrophiles. For the sake of simplicity, the former reaction is termed the alkenyl-aryl coupling, while the latter is termed the aryl-alkenyl coupling in this Handbook. Similar terms may be devised by linking the carbon groups of the organometal and organic electrophile with a dash in this order. 

B.i. Alkenyl-Aryl Coupling versus Aryl-Alkenyl Coupling... 

B.iii. Alkenyl-Aryl Coupling with Disubstituted Alkenylmetals... 

Table 3.5 Application of the Negishi coupling to the synthesis of natural products and other compounds of medicinal and agrochemical interest aryl-alkenyl and alkenyl-aryl coupling.

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