Alkynes additions

Reaction with additional alkyne releases an organic anthraquinone (128). Numerous TT-complexes are known. Examples include complexes of alkenes,... 

In a mechanism for the [67i+27t]/[67i+27i]/[2o +27t] process, the first two steps involved in this overall transformation were presumed to parallel the pathway observed for the above described [67t+27t], [67t+27t] process. A third cycloaddition of the cyclopropane unit with an additional alkyne component occurred via a [2[Pg.113]

New iridacyclobutadiene intermediates have been isolated in the [2+2+1+1] cycloaddition reaction that yields iridabenzene complexes from two alkynes, carbon monosulfide, and the metal (Section 2.12.5). The iridacyclobutadiene ring can be transformed, alternatively, into the corresponding r/s-cyclopcntadicnyl complex or into the iridabenzene product by reaction with additional alkyne, depending on the substituents present on both the iridacyclobutadiene ring and the incoming alkyne. 

Alkynes undergo combustion reactions and addition reactions, as alkenes do. In addition, alkynes undergo substitution reactions with metals. 

Without question, the metal-promoted cycloaddition of three alkynes to produce benzenes is the most extensively studied organometallic cycloaddition in intramolecular versions. Early work indicated the utility of Ni° systems e.g. Ni(CO)2(PPh3)2), Ziegler catalysts and rhodacyclopentadienes in the partially intramolecular cocycloaddition of a,b>-diynes with additional alkynes. Ziegler catalysts were noteworthy in giving rise to products containing the benzocyclobutene moiety from reactions of 1,5-hex-adiyne, while the Rh systems showed considerable utility in the preparation of anthraquinone derivatives from appropriate diyne precursors (Scheme 29). 

Chemoselectivity in cocycloadditions is typically poor unless the additional alkyne is resistant to simple cyclotrimerization. Examples of alkynes which satisfactorily fulfill this requirement include MesSiCBCSiMes, Me3SiC COMe and Me3SnC CSnMe3. In the case of the unsymmetrical alkyne. 

Besides addition, alkynes undergo certain reactions that are due to the acidity of a hydrogen atom held by triply-bonded carbon. 

Intermediate 2 can coordinate an additional alkyne (or olefin) to give 5 after insertion into the Ni-C bond (Scheme 7). Reductive elimination affords the corresponding cyclodecatriene derivative. Several related stoichiometric reactions with certain Ni complexes and alkynes or allene have been observed, thus confirming the proposed catalytic cycle (route ( )) [48] (eqs. (17) and (18)). 

In more complex reaction cascades an additional alkyne-insertion step can occur. Thus starting with intramolecular carbopalladation of a vinyl iodide to a carbon-carbon triple bond, followed by two intramolecular alkene-insertion steps and termination with dehydropalladation, a palladium-catalyzed synthesis of l-(5 -methylbicyclo[3.1.0]hex-T-yl)-5,5-bis(carboethoxy)cyclo-hexadiene (52) starting from l-iodo-4,4-bis(carboethoxy)-ll-methyldodeca-l,ll-dien-6-yne (51) is achieved. ... 

In a reaction completely analogous to the pyridone synthesis in Scheme 33, 5-nickelafuranones formed from Ni°, an alkyne and carbon dioxide (see Section 9.4.3.3) react with additional alkyne to give 2-py-rones (Scheme Under catalytic conditions this becomes a viable synthesis of the heterocycle be-... 

The strong forward donation-back donation of electrons (i.e., the Chatt model) between alkynes and ruthenium makes such a bond a very good ligand for Ru. Hence it is not surprising that reactions involving ruthenacyclopentadienes as intermediates, notably in the trimerization of alkynes to benzenes, occur readily. Intercepting the ruthenacyclopentadiene prior to its reaction with an additional alkyne, however, is rather rare. A unique juxtaposition of functionality occurs when a propargyl alcohol is the alkyne partner which allows such a diversion as shown in Scheme 1.3. 

Fuchs has examined a number of additional alkynes. One in particular, silyl-substituted triflone 104, may prove most useful, as it provides silylated alkyne products upon reaction with suitable substrates [62c]. In general, attempts to functionalize triflones with other groups at the alkyne carbon or at propargylic positions were unsuccessful. Triflones with more remote functionality, including bis-acetylenes, gave useful reagents. Fuchs triflone methodology can also be extended to vinylation and allylation reactions (Scheme 23) [63, 64). 

Reaction of hydrogen sulphite ions with alkenes, in the presence of either oxygen or peroxides170-177, produces a reasonable yield of the sulphonic acid salt (equation 24), formed by anti-Markovnikov addition. Alkynes also undergo a similar reaction178, except in this case a disulphonate salt is formed (equation 25). 

The use of trimethyl aluminum or lower reaction temperatures can slow the reductive elimination and/or promote the second insertion of additional alkynes into the carbon-nickel bond to give the dienylated product. One limitation to this reaction was that terminal alkynes were not applicable to this reaction due to rapid oligo/trimerization. 

An atom-economic Pd(II)-catalyzed addition/alkyne-aUene isomeriza-tion/IMDA reaction provided an efficient synthesis of highly functionalized bicycles with high regio- and stereoselectivity (14OL1208). 

The title compounds are generally obtained in good yields. The unsubstituted 4H-thiochromen-4-one core is accessible by employing trimethyl-silyl acetylene, where the TMS group is cleaved prior to the Michael addition. Alkynes with electron-donating and electroneutral groups are well tolerated, while electron-deficient (hetero)aryl substituents result in substantially lower yields. 

The couplings of di5mes with a third unsaturated component are described in several subsections throughout Section 1.1.3. However, several other processes merit discussion here that do not fall into the other categories described. The hydrosilylation of diynes provides an excellent route to cyclic dienylsilanes. A mechanism was proposed that involves Si—H oxidative addition, alkyne sUylmetalation, allgme insertion, and C—H bond reductive elimination to give 59 (Scheme A related process ensues when diynes are treat-... 

An extension of Hashmi s Au(III)-catalyzed phenol synthesis [81] to furan substrates 9 bearing an additional alkyne moiety allowed the preparation of C6-C7-heterofused benzofuran 11 (Scheme 9.3) [82]. According to the proposed mechanism, the Au(III)-catalyzed arene formation reaction generates o-alkynylphenol 10. A subsequent Au(III)-catalyzed cycloisomerization of the latter, following the general mechanism for an intramolecular nucleophilic addition of heteroatom to transition metal-activated carbon-carbon multiple bonds, gives 11 (Scheme 9.3). 

In Section 10.4.3, the 7r-bond of an alkene reacted as a Lewis base with the H-B unit of a borane (Lewis acid) via a four-center transition state to give an alkyl-borane. Alkynes are expected to react similarly, but the presence of the second ji-bond of the alk5me will lead to a vinylborane product. A primary vinylbo-rane can be (RCH=CHBH2), but this can react with additional alkyne to give... 

Stabilized Sulfur Ylides. Acid chlorides, anhydrides, and isocyanates acylate EDSA to generate good yields of stabilized sulfur ylides. In addition, alkynes conjugated with either ketones or esters react in a similar fashion (eq 2). ... 

The formation of 2-alkenyl-substituted furans was observed in the palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones. This reaction involved oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, P-hydride elimination, and catalyst regeneration (13JA13502). 

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