Addition of alkynes

On the other hand, Chen and Li reported a facile and selective copper-palladium-catalyzed addition of terminal alkynes to activated alkynes in water without the competition of the homocoupling of the terminal alkynes (Eq. 4.79). Subsequently, a simple and highly efficient Pd-catalyzed addition of a terminal alkyne to a C—C double bond, such as a conjugated enone, either in water or in acetone, was also developed (Eq. 4.80). A variety of 

---

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

Furans, thiophenes and pyrroles have all been obtained by addition of alkynic dienophiles to a variety of other five-membered heterocycles, as illustrated in Scheme 104. As the alkynic moiety provides carbons 3 and 4 of the resulting heterocycle, this synthetic approach provides an attractive way of introducing carbonyl containing substituents at these positions, especially as many of the heterocyclic substrates are readily generated. Such reactions do... 

Addition of alkynes to a-alkoxy aldehydes is most favorably performed with the corresponding zinc reagents (Table 12)46. As with Grignard reagents, the chelation-controlled addition of zinc alkynes proceeds with higher diastereoselectivity when diethyl ether rather than tetrahydrofuran is used as reaction solvent. 

In 2002, Braga el al. employed a chiral C2-symmetric oxazolidine disulfide as a ligand for the enantioselective synthesis of propargylic alcohols by direct addition of alkynes to aldehydes (Scheme 3.64). Good yields but moderate enantioselectivities (<58% ee) were obtained for the enantioselective alkyny-lation of aldehydes in the presence of ZnEt2. 

This chemistry was developed with the specific intention of application to the synthesis of phenols. There had only been one previous example of the addition of alkynes to 774-vinylketene complexes yielding phenols,22 despite a cornucopia of other organic fragments having been isolated from such reactions (see Sections II, V, and VI). The best results were obtained on reaction of the 3-phenylvinylketene complex 114.a with several alkynes. 

These results reveal that the a-isomer is thermodynamically more stable than the )3-iso-mer. The radicals so generated are trapped with TEMPO and diaryl diselenides. The addition of alkynes gives rise to vinylic tellurides. 

CuOTf/PyBox System The first direct asymmetric addition of alkynes to imines, generated from aldehydes and amines in situ, was reported by using copper salts in the presence of chiral PyBox ligand (Scheme 5.2). The products were obtained in good yields and excellent enantioselectivities in most cases. When toluene was used as solvent, up to 93% yield and 99% ee were obtained. Up to 99.5% ee was obtained when the reaction was carried out in 1,2-dichloroethane. The reaction can also be performed in water smoothly, and good enantioselectivities (78-91% ee) were obtained. 

Scheme 5.2. Asymmetric addition of alkynes to imines generated from aldehydes and amines.

Although the CuBr/QUINAP system is an effective chiral catalyst in alkynylation of imines or iminiums, one drawback is that enantiopure QUINAP is quite expensive. An analog of QUINAP, PINAP (Figure 5.2), was readily synthesized and found as a very effective chiral ligand in the direct addition of alkynes to iminiums generated from aldehydes and secondary amines in situ (Scheme 5.8). ... 

Preparation of cis-alkenes Lindlar s catalyst, which is also known as poisoned catalyst, consists of barium sulphate, palladium and quinoline, and is used in selective and partial hydrogenation of alkynes to produce c/s-alkenes. Hydrogen atoms are delivered simultaneously to the same side of the alkyne, resulting in syn addition (cw-alkenes). Thus, the syn addition of alkyne follows same procedure as the catalytic hydrogenation of alkyne. 

Asymmetric conjugate addition is a powerful method for the construction of ternary stereogenic centers. Erick Carreria of the ETH-Honggerberg, Zurich reports (Organic Lett. 2004,6,2281) the chiral-auxiliary mediated conjugate addition of alkynes to alkylidene malonate derivatives such as 1, to give, after hydrolysis and decarboxylation, the enantiomerically-enriched acid 3. 

Another useful reaction exemplified for the spirophosphorane (185), which is in equilibrium with the phosphorus compound (186 P-CN = 3), is the addition of alkynes. This gives a phosphorane with an alkene substituent (187 Scheme 30) (80TL925). 

The compounds (Bu 0)3 W=CR are alkyne metathesis catalysts.280 281 Probable intermediates in these reactions are tungstacyclobutadienes and the latter are seen in the presence of Cl ligands.282 Addition of alkynes to the latter leads to the formation of substituted r/ -cyclopentadiene derivatives... 

In this case a reaction sequence involving reductive elimination of H2 from Complex XV followed by insertion of alkyne into the remaining Pt-H bond, addition of alkyne to the Pt-Pt bond of the proposed diplatinum(I) intermediate, and then abstraction of chloride from the solvent is probable. Work is in progress to isolate and characterize proposed intermediates in this sequence, as well as to study the reactions in nonchlorinated solvents. 

A ruthenium-catalysed, three-component addition of alkyne to x./i-un saturated ketones to produce 1,5-diketones has been developed (Scheme 32).113... 

The rhodium-catalysed addition of alkynes to 1,2-diketones, 1,2-keto esters, and aldehydes has provided a method for the synthesis of tertiary alkynyl alcohols under... 

Addition of alkynes to imines generated in situ can lead to quinolines when the reaction is conducted in the presence of copper chloride [126] or montmorillonite clay doped with copper bromide [127]. In the latter case, the reaction was performed under solvent-free conditions and was microwave assisted (Scheme 8.57). 

The regioselectivity of the reaction depends on electronic and steric effects and is somewhat predictable. For example, the addition of alkynes to azides, which is an interesting reaction for the generation of 1,2,3-triazole libraries by the simple reaction of two molecules leads to regioisomers ... 

However, a reexamination of the first stage showed that PPh3 did not abstract chlorine from (ClsSi PtLa, but rather that adventious moisture produced a cyclodisiloxane (XX) with properties similar to those reported for complex (XVIII) no addition of alkyne could be effected (entry 122). 

A compound having the central skeleton depicted by X is known for (Bu 0)4W2(/i-C2Ph2)2 (35). Addition of alkynes to the tungsten dl—dl... 

---