Alkynes unactivated alkyne addition

Hydration of unactivated alkynes is an important method for functionalizing this plentiful hydrocarbon source. Therefore, a variety of metal ions have been proposed as catalysts for this reaction, and almost all of the reported additions of water to terminal alkynes follow the Markonikov rule. The hydration of l-aUcynes with Hg(II) salts in sulfuric acid [85], RuCh/aq.HCl [86, 87], K[Ru (edta-H)Cl] 2H20 [88], RhCl,.3H20/aq. HCl [89], RhCl3/NR4 [90], Zeise-type Pt(II) complexes [91-93], and NaAuCl4 [94] produced exclusively methyl ketones (Eq. 6.46). 

In aqueous media, the addition of unactivated alkynes to unactivated alkenes to form Alder-ene products has been realized by using a ruthenium catalyst (Eq. 3.44).180 A polar medium (DMF H20 = 1 1) favors the reaction and benefits the selectivity. The reaction was proposed to proceed via a ruthenacycle intermediate. 

We initially observed an addition reaction of tertiary phosphines to unactivated alkynes. The method was then applied to reactive alkenes, allenes and 1,3-dienes, and finally to unactivated alkenes (Scheme 4). Such a step-up methodology turned out to be effective in this study. 

Zirconocene diiodide can promote the addition of diallylzinc to a,/1-disubstituted unactivated alkynes. Thus, in the case of 5-decyne, a 94/6 mixture of the two isomeric alkenyl iodides (derived respectively from syn and anti additions to the triple bond) was obtained after iodinolysis (equation 74)108. However, the stereoselectivity was lower for 2-butyne (80/20) and the case of unsymmetrical alkynes was not mentioned. 

Resin-bound amines can be converted into imines [710,711] or enamines by reaction with carbonyl compounds (Entries 6 and 7, Table 3.39). Resin-bound enamines have also been prepared by Michael addition of resin-bound secondary amines to acceptor-substituted alkynes [712], by Hg(II)-catalyzed addition of resin-bound secondary amines to unactivated alkynes [713], by addition of C-nucleophiles to resin-bound imino ethers [714], and by chemical modification of other resin-bound enamines [712,713,715], Acceptor-substituted enamines ( push-pull alkenes) are not always susceptible to hydrolytic cleavage by TFA alone and might require aqueous acids to undergo hydrolysis [716]. 

The use of Sc(OTf)2 and SnCl2/SDS systems enables the reaction with imines in water.157,158 The allylmetallation of simple unactivated alkynes is not easy, and proceeds usually with poor regio- and stereoselectivity. ZrCl4-catalyzed allylstannylation of unactivated alkynes, however, proceeds with high regio- and stereoselectivities ( A-addition) (Equation (48)).159... 

Although the addition of methanol to electron-deficient alkynes such as acetylene dicarboxylates is easy, the intermolecular addition of alcohol to unactivated alkynes in the presence of ruthenium catalysts to form enol ethers is not straightforward, and the only reported examples concern the addition of allylic alcohols to terminal alkynes. Thus, in the presence of a catalytic amount of RuCl(tris(pyrazolyl)borate)-(pyridine)2, allyl alcohol adds to phenylacetylene in refluxing toluene to produce a 1 1 mixture of allyl /3-styryl ether and 2-phenylpent-4-enal (resulting from Claisen rearrangement) (Scheme 8.7) [17]. 

A new example of carbometalation is the HfCU-catalyzed franx-addition of allylsi-lane to unactivated alkynes (Eq. 24) [26]. The mechanism proposed for this regio-and stereoselective formation of silylated 1,4-dienes is illustrated in Fig. 11. 

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