Internal alkynes dimer

This type of alkyne dimerization is also catalyzed by certain nickel complexes, as well as other catalysts and has been carried out internally to convert diynes to large-ring cycloalkynes with an exocyclic double bond. ... 

The cross-dimerization of various electron-rich 1-alkynes 5 with electron-deficient internal alkynes such as methyl phenylpropiolate 6 was promoted by an [lrCl(cod)]2 combined with bidentate phosphine ligands such as (racj-BlNAP (Equation 10.2) [16]. This reaction produces a 1 1 adduct 7 in high regioselectivity and stereoselectivity. 

Aryl acetylenes undergo dimerization to give 1-aryl naphthalenes at 180 °C in the presence of ruthenium and rhodium porphyrin complexes. The reaction proceeds via a metal vinylidene intermediate, which undergoes [4 + 2]-cycloaddition vdth the same terminal alkyne or another internal alkyne, and then H migration and aromatization furnish naphthalene products [28] (Scheme 6.29). 

H-shift is invoked for the formation of 6 and regeneration of catalyst 8. The proposed mechanism is unusual insofar as the tt-bonds of electroneutral alkynes and arenes seldom participate in Diels-Alder reactions. The intermediacy of metal vinylidenes is supported by the failure of internal alkynes to dimerize under the reported conditions. More importantly, mechanistic restrictions imposed by the porphyrin ligand set severely restrict conceivable alternative mechanisms. 

Finally, it can be noted that some cross-dimerization of terminal alkynes with internal alkynes, where ruthenium vinylidene intermediates are postulated, have also been reported [74, 75]. 

Both amido and pinacol derivatives of B-Si compounds 125 and 126 added to terminal and internal alkynes in the presence of a palladium244-246 or platinum(O) catalyst247 by a mechanism involving an oxidative addition-insertion process (Equation (39)).248 On the other hand, phosphine-free nickel(O) catalyst resulted in the dimerization of alkynes giving a Z,Z-isomer of l-silyl-4-borylbutadiene derivatives.249 Since the palladium-catalyzed cross-coupling at the C-B bond is faster than the G-Si bond of 137, a silylboration-cross-coupling sequence provided a method for the synthesis of 1-alkenylsilanes.246... 

Cyclic seven-membered vinyl silanes 161 were obtained by regio- and stereoselective hydrosilylation of internal alkynes catalyzed by the ruthenium complex [Cp Ru(MeCN)3]PF6, as shown in Equation (33) <2005JA10028>. Hydrosilylation of 2,2-divinyladamantane with bis(hydrosilane) species 162 in the presence of Zeise s dimer [Pt2Cl4(CH2CH2)2] gave the disilacyclic 163 in high yields (Equation 34) <19980M4267>. 

Reductive dimerization of two alkyne moieties with dihydrogen forming 1,3-dienes (together with linear and cyclic trienes and tetraenes) is catalyzed by [Cointernal alkynes, such as diphenylcthync and 2-butyne. c i.s-addition products are formed. 

Alkyne metathesis is generally restricted to internal alkynes, and is driven to completion by the evolution of gaseous 2-butyne. Representative examples of alkyne cross-metathesis are depicted in Scheme 33, and include (i) dimerization of alkynylbenzoic acid derivative 287, (ii) alkyne cross-metathesis of 289 and bis(trimethylsilyl)acetylene, (iii) cross-metathesis of enyne 291 and various alkynes and metathesis dimerization of 291, and (iv) formation of high molecular weight alkyne-containing polymers through acyclic diyne metathesis (ADIMET) polymerization of acyclic diynes (e.g., 293) " using the molybdenum hexacarbonyl/2-chlorophe-nol system. 

It is important to note that unlike the disiamylborane dimer [4] and the dibro-moborane-dimethylsulfide complex [5], (9-BBN)2 does not exhibit a large increase of relative reactivities toward alkynes. The relative reactivity of 1-hexyne is only one seventh that of 1 -hexene, and 3-hexyne shows about the same relative reactivity as does ds-3-hexene. Consequently, one can selectively hydroborate the terminal alkene in the presence of internal alkyne [6]. 

Iridium dimer complexes catalyse the 3 + 2-cycloaddition reactions of organic azides with bromoalkynes to furnish 1,5-disubstituted 4-bromo-1,2,3-triazoles in excellent yields under mild conditions. Ruthenium(II)-azido complexes undergo 3 + 2-cycloaddition reactions with strained cyclooctynes under ambient temperatures. No reaction was observed with non-activated terminal or internal alkynes under the same conditions. Dithioic acid copper catalysts (60) catalyse the 3 + 2-cycloaddition reaction of azides with alkynes to form 1,4-disubstituted-1,2,3-triazoles in various solvents and under various temperatures. Thermal Huisgen 3 + 2-cycloaddition reactions of azides and bis(trimethylsilyl)acetylene formed 4,5-bis(trimethylsilyl)-l/f-l,2,3-triazoles in low to high yields (15-95%). The Cu(I)-catalysed 3 + 2-cycloaddition... 

Formation of alkyne dimers with a GO inserted was observed in the thermal reactions of Fe3(GO)i2 with isopropenyl-acetylene two isomeric open clusters 3a and 3b were isolated and characterized by X-ray diffraction. In contrast, the thermal reactions of internal propargylic alcohols with Fe3(GO)i2 led to pentanuclear acetylide derivatives, obtained upon elimination of aldehydes or chetones from the alkynes (Figure 1). ... 

Selective intermolecular [2 - - 2 - - 2] cycloaddition of terminal alkynes is more difficult to achieve than internal alkynes, due to their various reactivities toward transition-metal complexes in addition to the regioselectivity problem. Indeed, a neutral rhodium(I)/phosphine complex such as RhCl(PPh3)3 generally reacts with terminal alkynes to give not cyclotrimers but linear dimers [20]. The neutral rhodium(I) and rhodium(III) complexes could be applied to intermolecular [2 - - 2 - - 2] cycloaddition of terminal alkynes (Scheme 4.5) [13,15a and b]. 

Silaborative dimerization of two molecules of internal alkynes in the presence of a silylborate is catalyzed by Ni(0) generated in situ [155],... 

The platinum-catalyzed hydration reactions of alkynes have been recently reviewed [ 1 a, e]. The early works in this field refer to the use of simple platmum(II) halides or of Zeise s Pt(II) dimer, [ PtCl2(C2H4)2 2], as active and selective catalysts for the hydration of unactivated terminal and internal alkynes [123-125] (Scheme 68). Unfortunately, for unsymmetrically substituted alkynes, the reported regioselec-tivities are poor. 

We had established in previous catalytic reactions involving complex 24 that this precatalyst was activated by the removal of the cod (1,5-cyclooctadiene) from the ruthenium by its reaction with the alkyne substrate via a [2 + 2 + 2] cydization as illustrated in Equation 1.64 [57]. Thus, not only does this reaction constitute an activation of the Ru complex 24 by reacting off the cod, it also serves as a novel atom economic reaction in its own right. Both internal and terminal alkynes participate. The overall atom economy of this process is outstanding since cod itself is simply available by the nickel-catalyzed dimerization of butadiene. Thus, the tricyclic product is available by the simple addition to two molecules of butadiene and an alkyne with anything else only needed catalytically. 

An orthometallated complex was obtained from dibenzylamine and Pd(OAc)2, subsequent reaction with NaBr gives a bridged dimer [Pd(/x-OAc) G6H4(GH2NHGH2Ph)-2 ]2 Insertion reactions with alkynes were carried out. It is noted that double insertion can occur. Furthermore, reactions with Tl(acac), PPh3NH(GH2Ph)2, and AgX were studied. Internal acetylenes can be inserted into orthopalladated a-methylbenzylamine. Double and tri-insertion may occur depending on the alkyne. 

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