Cross-coupled dienes

The alkenyl(phenyl) iodonium salt 725 undergoes the facile cross-coupling with vinylstannane to form the conjugated diene 726[594]. 

Scheme 16 Construction of a nine-membered cyclic ether with a (Z,Z)-1,3-diene unit by sequential RCM and silicon-assisted intramolecular cross coupling in Denmark s synthesis of brasilenyne (85) [65]...

A cross-coupling reactions of terminal alkynes with terminal alkenes 32 supported on Merrifield-resin (Scheme 4.5) in the presence of Grubs ruthenium initiator [Cl2(PCy3)2Ru = CHPh] provided efficient access to supported 1,3-dienes 33 which were transformed into octahydrobenzazepinones 34 via MeAlCl2 catalyzed Diels-Alder reaction [27]. 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

Bromoalkynes also couple with vinylstannanes readily to result in enynes. Synthesis of protected enynals via cross-coupling of vinylstannanes with 1-bromoalkynes in the presence of a catalytic amount of Pd(II) has been reported (equation 143)252. Hiyama and coworkers extended the Stille methodology for sequential three-component coupling of trimethylstannyl(trimethylsilyl)acetylene with a vinyl iodide in the first step and cross-coupling of the intermediate trimethylsilylethyne with another alkenyl iodide in the presence of tris(diethylamino)sulphonium trimethyldifluorosilicate in the second step to generate a dienyne (equation 144)253. Both steps occur under palladium catalysis, in one-pot, to result in stereodefined l,5-dien-3-ynes. 

Tetraalkylstannanes with double bonds at allylic or more remote positions undergo cross-coupling with allylsilanes to yield dienes, as illustrated in reaction 47299. 

Palladium-catalyzed cross-coupling of 19 with allyl bromide occurs exclusively at the vinylstannane moiety to give 1-ethoxy-1-silyl-1,4-diene 20. The following ether exchange with allyl alcohol causes the Glaisen rearrangement to give an acylsilane derivative 21 (Scheme 64).2... 

Coupling of vinyl halides with vinyltin reagents. This cross-coupling can be effected at room temperature in DMF in the presence of (CH,CN)2PdCl, or CLPd[P(C6H5),]2. Pure (E,E)-, (E,Z)-, (Z,E)-, or (Z,Z)-1,3 dienes can be prepared by this reaction, since the geometry of each partner is retained. The reaction tolerates many functional groups. 

Cross-Coupling Reactions of Allenes Producing Compounds with an I ntact 1,2-Diene Moiety... 

The transition metal cross-couplings of allenes described here offer practical solutions for the modification of 1,2-dienes and access to the preparation of highly functionalized 1,3-dienes, alkynes and alkenes, which are often not easily accessible in a regio- and stereoselective manner by classical methods. Some of the prepared alkynes or functionalized allenes serve as important intermediates in syntheses of natural products, biologically active compounds, e.g. enynes and enyne-allenes, and new materials. It can be predicted that further synthetic efforts will surely be focused on new applications of allenes in transition metal-catalyzed cross-coupling reactions. 

The cross-coupling reaction between an allene and an acetylene takes place at the terminal double bond of an allene to generate a titanacyde, which, on treatment with electrophiles, gives diverse 1,4-dienes in a highly stereoselective manner (Scheme 16.100) [105],... 

Scheme 16.100 Preparation of 1,4-dienes via Ti-mediated cross-coupling reaction.

Cross-Coupling Reactions of Allenes Producing Compounds with an Intact 1,2-Diene Moiety 849 Cross-Coupling Reactions of Allenyl Halides 849 Cross-Coupling Reactions of Allenylmetal Compounds 856 Cross-Coupling Reactions of a-Substituted Allenes 860 Cross-Coupling Reactions of Allenes at the Central Position 862 Synthesis of Alkynes 870 Miscellaneous Reactions 872 Conclusion 873... 

---