Alkyl alkynes

ALKYL-1 -ALKYNES, 58, 1 /V-Alkylhydroxy I amines, 58, 108 ALKYL ARYL SULFIDES, 58, 143 Alkyl aryl thioethers, 58, 145 C-ALKYLATION, phase transfer catalysis... 

Complexes 59 and 60 catalyse the hydrosilylation of phenylacetylene (but not other terminal alkyl alkynes) with HSi(Me)jPh. Generally, the Rh analogue is more active than the relative Ir. Both catalysts gave mixtures of all regioisomers, with a preference for the p-Z-isomer, in contrast to what has been reported with other non-NHC cationic complexes of Rh, where the p-f isomers are predominating. Here also the exact nature of the catalytic species is unclear [48],... 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

Both alkynes and alkenes can be obtained from adducts of terminal alkynes and boranes. Reaction with iodine induces migration and results in the formation of the alkylated alkyne.32... 

As indicated in Scheme 78, ortho-, meta-, and -substituted aryl alkynes were studied and were all shown to be effective two carbon components in this process. Alkyl alkynes were also studied and were found to give moderate yields of the [5 + 2 + 1 + l]-products (Equations (49) and (50)). 

Very recently Ryu and coworkers disclosed radical carbonylation/Sonogashira coupling sequences (Fig. 44) [218]. The reaction is applicable to primary, secondary, and tertiary alkyl iodides 177, and terminal aryl or alkyl alkynes 185. Alkynyl... 

Alt and co-workers have prepared numerous alkyl (67) and acyl (68) tungsten(II) alkyne complexes. A definitive paper detailing these results was published in 1985 (69). The reaction sequence which converts CpW-(CO)3R and free alkyne to CpW(CO)(RC=CR)R and free CO is not simple. Low temperature photolysis (-30°C) of the reagents in pentane first yields acyl alkyne products [Eq. (15)]. These products result from trapping of the initial alkyl alkyne derivative which rapidly reacts with CO to form the observed acyl product [Eq. (16), L = CO] (69). 

Independent experiments show that the alkyl alkyne undergoes alkyl migration to carbon monoxide at — 100°C where the acyl can be trapped with phosphine, phosphite, or free carbon monoxide. Although the alkyl alkyne is converted to the acyl derivative by scavenging CO under the photolytic reaction conditions, these same alkyl derivatives can be isolated following thermal disproportionation of the acyl for a few minutes in refluxing toluene. Evidently thermal loss of CO from CpW(CO)-(HC=CH)[C(0)Me] promotes alkyl migration from the acyl back to the... 

Cp(CO)2M[CR=CRC(R)6] with M = Mo, W Cp = tj5-C5H5, tj5-C5H4Me, or i75-C9H7 and R = Me, Et, "Pr, or "Bu (70). The net conversion of CpM(CO)3R reagents plus alkyne to the alkenylketone products [Eq. (57)] corresponds to 1 1 adduct formation, but the reaction is mechanistically complex. Formation of alkyl alkyne and acyl alkyne complexes with loss of CO precedes addition of CO to form the final product. 

Aromatic, n-alkyl, and branched alkyl alkynic ketones are effectively reduced (eq 4). 

A highly flexible catalytic one-pot procedure for the synthesis of indoles employing or/ o-chloro-substituted l-phenyl-2-alkyl-alkynes or phenyl(aminoalkyl)alkynes as starting materials through a reaction catalyzed by Cp2TiMe2 has been reported.1916... 

Benzenetellurinyl trifluoromethanesulfonate (155) reacts with internal alkynes in acetonitrile to afford oxazoles via a spontaneous intramolecular cyclization of the initially formed addition products (156) <92CC1070>. The reactions with aryl alkyl alkynes are regioselective. The addition products from terminal alkynes do not cyclize, but isomerize to stable (Z)-alkenes instead. The pathway shown in Scheme 72 accounts for the products. 

Reactivity studies of jj -acyl complexes are limited. Compounds (115) react with CO to afford octahedral cis,trans -acyl complexes (121), probably via prior conversion to a coordinatively unsaturated monodentate see Monodentate Ligand) acyl (equation 27). The cis,trans- 2 ) then isomer-izes to trans,trans- i2 ). Phenylacetylene reacts with (115 R = R = Et) to give a mixture of acyl-alkyne coupling products,that is (122). Reaction with the R = i-Pr compound proceeds in a different way, by equilibration to the -alkyl, followed by alkyl-alkyne coupling, and finally CO insertion to give rj -acyl complex (123). ... 

Substituted NHCs have been used as ligands under various conditions and with widely variable success. For example, Batey used NHC-precursors with pendant carbonyl groups that could induce a stronger acidity of the C—H bond in position C-2, and allow for a faster generation of the free carbene under basic reaction conditions [60], Under neutral reaction conditions, however, a rather unusual complex was isolated and used, along with free PPhs, for the coupling of aryl bromides and iodides with both aryl and alkyl alkynes (Scheme 6.11). 

Indoles can also be prepared directly from o-chlorophenyl-2-alkyl alkynes and primary amines via a tandem alkyne hydroamination/Buchwald-Hartwig iV-arylation sequence, as illustrated for the conversion of 7 to 8 via intermediate enamine 9. ... 

Another example of the iron-catalyzed carbometallation reaction of unactivated alkynes was reported for the aryknagnesiation of alkyl(aryl)acetylenes [64b]. The addition of arylmagnesium bromide to the disubstituted aryl(alkyl)alkynes 234 was found to proceed efficiently in the presence of Fe(acac)j as a catalyst and a substoichiometric amount of an N-heterocyclic carbene (NHC) ligand (IPr) as an additive, which significantly increased the yield of this carbometallation process (Scheme 10.79). 

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