Alkyne derivatives coupling

Having pyrazinylacetylenes in hand, one could convert the alkynyne functionality into the corresponding ketone via hydration [33], Thus, the coupling of iodide 36 and acetylene 37 produced pyrazinylalkyne 38. Subsequent exposure of 38 to aqueous sodium sulfide and aqueous hydrochloric acid in methanol led to ketone 39. Such a maneuver provides additional opportunities for further manipulation of the alkynes derived from the Sonogashira coupling reactions. 

Several of the synthetic methods appropriate to these compounds have already been described as applicable to small rings (cyclization by metalloid hydride addition to alkenes and alkynes, and coupling through metal halide elimination). While much of the chemistry of these compounds is similar to that of acyclic derivatives, a few peculiarities are worthy... 

The use of a PdCl2(PPh3)2-InBr3 reagent system catalyzes cross-coupling reactions of a variety of aryl iodides with several terminal alkynes. The corresponding functionalized alkyne derivatives are produced in good yields (Scheme 102) 351... 

An X-ray crystallographic investigation 116) of Co4(CO)io(EtC2Et) has revealed the structure shown in (VI). The structure is derived from that of the parent carbonyl, Co4(CO)i2> by substitution of two bridging carbonyl groups with an alkyne unit coupled with a substantial modification of the C04 skeleton. The structure is different from that first postulated for Co4(CO)io(RC2R ) complexes, where it was assumed that the basic tetrahedron of cobalt atoms remained intact 48, 117). 

The Pd-catalyzed coupling reactions of alkenyl bromides with heterocyclic alkynes (40) under the above phase-transfer conditions have been employed to prepare a large number of heterocyclic alkyne derivatives, including some naturally occurring compounds (Scheme 28). The experiment conditions... 

Asymmetric synthesis of nucleosides via molybdenum-catalyzed alkynol cycloisomerization coupled with stereoselective glycosylations of deoxyfuranose glycals and 3-amidofuranose glycals. Journal of the American Chemical Society, 118, 6648-6659 (b) McDonald, F.E. and Chatterjee, A.K. (1997) Group VI metal-promoted endo-azacyclizations via alkyne-derived metal vinylidene carbenes. Tetrahedron Letters, 38, 7687-7690 ... 

Reductive coupling of two CO ligands to form a coordinated alkyne derivative, e.g. treatment of the Ta complex [Ta(CO)2-(dmpe)2Cl] with activated Zn dust in thf and then with MesSiCl gave a 25% yield of [Ta(Me3SiOC=COSiMe3)(dmpe)2Cl] which can in turn be hydrolysed to the corresponding complex of the novel dihydroxyacetylene, HOC=COH. ... 

Schreiber s early efforts in this area were focused on libraries of compounds having structural features reminiscent of rigid, complex, stereochemically rich natural products. In a key early example, solid-phase split-pool synthesis was used to generate a combinatorial library of over two million complex, polycyclic compounds derived from shikimic acid [17]. A stereoselective tandem acylation-nitrone cycloaddition was used to generate 18 tetracyclic scaffolds, to which 30 alkynes were coupled using a Sonogashira reaction, 62 amines were coupled via y -lactone aminolysis, and 62 carboxylic acids were coupled by alcohol esterification (Fig. 9.1-3(c)). In addition, a portion of the solid supports were left unreacted at each of the last three steps to generate a skip codon that further increased the diversity of the library. 

We have completed the first total synthesis of (-)-ichthyothereol (46) and its acetate 47 by the palladium-catalyzed coupling reaction between the ( )-iodoolefin 63 and the triyne derivative 66. The iodoolefin 63 was prepared from commercially available diethyl L-tartrate through the Co2(CO)8-mediated endo cyclization of the optically active c/.v-epoxy-alkyne derivative 60 in a highly stereoselective manner. 

Miura. ° Reaction of allg nes with benzamides in dioxane at 100 °C proceeded under total regio- and stereoselective control to provide the ort/zo-alkenylated product (Scheme 9). It was essential to add stoichiometric amounts of AcOH to obtain optimal yield. Reaction of benzamide with various alkynes proceeded smoothly to produce the desired products in moderate to good yields. The reaction of 1-phenyl-2-(trimethylsilyl)acetylene proceeded efficiently but it underwent desilylation to afford the 1,1-diarylethene in 63% yield. In addition, the catalytic system was found to be suitable to the coupling of phenylazoles and phenylimidazoles with several alkyne derivatives giving dialkenylated products. In contrast, the sterically more hindered l-methyl-2-phenylimidazole provided the mono-alkenylated product selectively as the sole product. ... 

Silyl and geimyl functionalised vinyl cyclopropenes ring-open thermally to give allene and alkyne derivatives with the former dominating, a-trimethylsilyl a-allenyl ketones couple to give enediynes related to the neocarzinostatin chromophore and also result fnnn Y-(t-BuMe2Si)allenylborane and acetylenic aldehydes. Allenylsilanes couple with AdQ and... 

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