Dimerization reactions alkynylation

The formation of butadiynes from bis(alkynyl)mercury compounds in the presence of a catalytic amount of RuHCl(CO)(PPh3)3 is closely related to the ruthenium-catalysed dimerization reaction in terms of the mechanism [60]. The proposed catalytic cycle involves the formation of a (alkynyl)(vinyli-... 

Dimerization of alkynyl enones (E or Z) in the presence of Ni(COD)2 catalyst and PhjP yield bicyclic compound chemoselectively and stereo selectively. Interestingly, the reaction can occur when a second enone is present to give the corresponding [2-1-2 -1-2] cycloaddition product in moderate yield [182]. 

The acetylide anion 3 is likely to form an alkynyl-copper complex by reaction with the cupric salt. By electron transfer the copper-II ion is reduced, while the acetylenic ligands dimerize to yield the -acetylene 2 ... 

In a reaction closely related to the latter, pyranylidene derivatives are obtained by the intermolecular radical coupling of alkynyl- or alkenylcarbene complexes and epoxides. Good diastereoselectivities are observed when cyclic epoxides are used. Moreover, the best results are reached by the generation of the alkyl radical using titanocene monochloride dimer [90] (Scheme 43). 

Ir-diphosphine complexes have been shown to catalyze a number of potentially interesting C—C coupling reactions [41]. Special mention should be made of the various transformations of alkynes (cycloaddition, isomerization, dimerization, alkynylation), selected aldol and carbonylation reactions, even though the synthetic potential of some of these reactions has not been explored. 

Under optimized conditions, cycloisomerizations of a number of functionalized hept-l-en-6-ynes took place in good-to-excellent yields (Table 9.3). Heteroatom substitution was tolerated both within the tether and on its periphery. Alkynyl silanes and selenides underwent rearrangement to provide cyclized products in moderate yield (entries 6 and 7). One example of seven-membered ring formation was reported (entry 5). Surprisingly, though, substitution was not tolerated on the alkene moiety of the reacting enyne. The authors surmize that steric congestion retards the desired [2 + 2]-cycloaddition reaction to the point that side reactions, such as alkyne dimerization, become dominant. 

Methylation of organomereurials.2 Alkenyl-, alkynyl-, and arylmcrcurials are methylated by 1 in HMPT in 90% yield. In theory I could serve as catalyst in alkylations with CH3I, but yields are lower because of interfering side reactions, mainly dimerization. Alkylmercurials are not reactive to I. 

Alkynyl(diisopropylsilyl)oxy-diazoacetates (295) undergo intramolecular 1,3-dipolar cycloaddition in good yield when R1 = H (isolation of silver pyrazolide 296 was possible) and R2,R2 = Me,Me or (CH2)5, but no reaction occurred when R = H, R2 = H or R1 = Me (340). The silicon substitution is apparently crucial. Replacement of the Si(i-Pr)2 in 295 (R1 = R2 = H) by Si(f-Bu)2 allowed an uncatalyzed intramolecular [3 + 2] cycloaddition to take place [xylene, 140-160°C, 11% yield (340)], while Ag(I) catalysis led to decomposition. A diazoacetic acid (2-propyn-l-yl)oxysilyl ester also produced a bicyclic pyrazole, but in low yield. On the other hand, the same diazo compound 295, which reacted intra-molecularly under silver ion catalysis, underwent dimerization by an mfermolecular... 

The reacuons of electrophihc tnflyl sources with nucleophiles were investi gated The reaction of tnfhc anhydride with an organolithium reagent is not synthetically promising because of ditnflylation and other side reactions [20] When phenyllithium reacts with tnfhc anhydnde, dimerization products and acetylenic Michael diadducts are observed [20] (equation 17), but using the sodium salt of the alkynes instead of the lithium salt provides the alkynyl tnfluoromethyl sulfones [21] (equation 18) (Table 7) Alkynyl tnfluoromethyl sulfones are of synthetic interest, because they show a pronounced reactivity toward nucleophiles in addition reactions and cyclopentadiene in Diels-Alder reactions [21] (Table 7)... 

Mononuclear ruthenium complexes have become useful catalysts, not only because they can have high regio- and stereoselectivity but also because their catalyzed reactions rely on an elucidated mechanism. This true for the cis-dihydride (PP3)RuH2 complex, a catalyst precursor for the selective head-to-head dimerization of phenylacetylene to the corresponding (Z)-enyne, via bis(alkynyl) active spe-... 

Dimethylpropynylindium (XLVIII) can be prepared by the reaction of dimethylindium chloride or bromide with sodium propynide as a colorless, crystalline substance 148). Whereas indium trimethyl is monomeric in benzene, the alkynyl compound is dimeric, but only sparingly soluble in this and other aprotic noncoordinating solvents. Improved solubility has been observed in diethyl ether due to the formation of a weak adduct 148). According to crystallographic data 148), compound XLVIII can be regarded as a coordination polymer in the solid state, as indicated in Fig. 10. The axial positions on the trigonal bipyramidal coordination polyhedron of each... 

Brummond et al. disclosed that acyclic allenynes could be efficiently converted into tetracyclic compounds via consecutive rhodium-catalyzed Alder-ene and double Diels-Alder cycloaddition reactions [47]. The former reaction transforms alkynyl allenes such as 45 into triene-ynes (46) using rhodium biscarbonyl chloride dimer. 

Dimeric association (71) can be obtained by an acid-base reaction between alkyl zirconocene and a terminal alkynyl ruthenium complex (equation 32). Surprisingly, the same reaction was observed with an iron acetylide opposed to Schwartz s reagent see Schwartz s Reagent) (equation 33). ... 

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