Cross-coupling reactions conjugated diene synthesis

Conjugated enynes are of importance for themselves, as well as for the synthesis of conjugated dienes. The cross-coupling reaction of 1-alkenyl(disiamyl)boranes (3c) with 1-bromo-l-alkynes (Scheme 2-34) provides conjugated enynes in high yields [45]. 

Synthesis of Conjugated Dienes. The cross-coupling reaction of alkenylboronates with alkenyl halides is a general method for the S3Uithesis of stereodefined 1,3-dienes (eq 11). ... 

This methodology appears quite general to synthesize differently substituted conjugate dienes and has been recently applied to the stereoselective synthesis of chiral 2-sulfinylated dienes via the Stille process [171], or nitrogenated dienes via Suzuki [172, 173] or Negishi cross-coupling reactions for instance [174, 175]. 

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... 

The Suzuki reaction provides a versatile, general method for the stereo- and regiospe-cific synthesis of conjugated dienes, enynes, aryl substituted alkenes, and biaryl compounds via Pd-catalyzed cross-coupling of vinyl halides or aryl halides with... 

Dienes. The (E)-l-alkcnylzirconium compounds, obtained by hydrozirconation of 1-alkynes (6, 177-178), undergo cross coupling with alkenyl halides to form conjugated dienes (cf. the similar reaction of alkcnylalanes with alkenyl halides, 7, 95-96). In the present synthesis tetrakis(triphenylphosphine)-palladium (6, 571-573) can usually serve as catalyst. Nickel catalysts are less effective than Pd catalysts in this case. ... 

Transition metal catalyzed reactions and in particular cross-couplings are commonly employed to access conjugated dienes. Recently, efforts have been devoted to the stereoselective synthesis of silylated, stannylated, or nitrogenated 1,3-dienes using such methods. 

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