Teiji Yanagi

Abstract The transition metal-catalyzed reactions of organometallics with organic halides have been extensively studied to prove a new approach to selective formation of carbon-carbon bonds. Recently, such coupling reactions of haloarenes with aryl magnesium1–3 and zinc4 compounds in the presence of palladium or nickel complexes have been reported for the synthesis of biaryls. Davidson and Triggs5 have previously reported that arylboronic acids react with sodium palladate to give the corresponding biaryls in good yields. The synthetic utility of the dimerization reaction is, however, limited because it requires stoichiometric amounts of the palladium compound. On the other hand, we have recently reported that cross-coupling reactions between alkenylboranes and organic halides such as alkenyl,6 alkynyl,6 aryl,7 allyl,8 and benzyl8 halides are effectively catalyzed by a catalytic amount of tetrakis(triphenylphosphine)palladium, Pd(PPh3)4 in the presence of suitable bases as indicated in Scheme 1. Although the detailed mechanistic pathway is not clear at present, the reaction should involve a transmetallation step from alkenylboranes to alkenylpalladiums.

Abstract (2E,4E)-, (2Z,4E)-, and (2E,4Z)-2,4-Alkadienoates can be synthesized in high yields by the cross-coupling of ethyl (E)-3-bromoacrylate, methyl (E)-3-bromo-2-methylpropenoate, ethyl (Z)-3-bromocrotonate,1-bromo-2-(ethoxycarbonyl)cyclohexene, and 4-bromocoumarin with 2-[(E)-1-alkenyl]-1,3,2-benzodioxaboroles or diisopropyl (Z)-1-hexenylboronate in the presence of 3 mol% of Pd(OAc)2, 6 mol% of PPh3, and 2 equivalents of Na2CO3 or K2CO3 in alcoholic solvents while retaining the original configuration of the double bonds in β-bromo esters and 1-alkenylboronates. Although the coupling reaction with 1-hexenylboronate with (Z)-3-bromoacrylate gave a mixture of ethyl (2Z,4E)- and (2E,4E)-nonadienoates in a ratio of 63 : 37, it was found that the use of bis(diphenylphosphino)ferrocene as a ligand of palladium brought about the stereoselective coupling under mild conditions.

Abstract The reaction of ketones with lithium thioalkynolates readily obtainable from corresponding acetylides and sulfur, followed by thermolysis gives trisubstituted olefins.

Abstract The conjugate addition of 1-alkenyl(disiamyl)boranes to α,β-unsaturated ketones, esters, or nitriles was carried out in the presence of Ni(acac)2 and triethylamine in DMF. The reactions provided γ,δ-unsaturated ketones, esters, and nitriles in high yields while retaining the original configuration of the 1-alkenylboranes. A similar addition reaction of 1-alkenyl(disiamyl)boranes to 1-acetyl-2-vinylcyclopropane produced the terminal and internal coupling products, 5,8-alkadien-2-on and 5-ethenyl-6-alken-2-on, in high yields in some cases with high regioselectivity favoring the terminal addition products.

Abstract (2E,4E)‐, (2Z,4E)‐ and (2E,4Z)‐2,4‐Alkadienoates can be synthesized in high yields by cross‐coupling of alkenes with alkenyl boron compounds in the presence of a Pd‐catalyst, Na 2 CO 3 or K 2 CO 3 and MeOH or EtOH.