Coupling of alkynes

Scheme 5.1-27 The zinc triflate-catalyzed coupling of alkynes with aldehydes to give propargyl alcohols in an ionic liquid.

Scheme 8.30 Nickel-catalyzed reductive coupling of alkynes with epoxides.

The influence of iron(III) salts on coupling reactions of alkynes and aldehydes (Scheme 10, routes B and C) was also explored. In these routes, a new stereoselective coupling of alkynes and aldehydes was unmasked, which led to ( ,Z)-1,5-dihalo-1,4-dienes (route B, Scheme 10) and/or ( )-a,p-unsamrated ketones (route C, Scheme 10) [27]. 

Another example of the addition of terminal alkynes to C=N in water is the coupling of alkynes with in-situ-generated A-acylimines (Eq. 4.32) and A-acyliminium ions (Eq. 4.33). In 2002, Li et al. developed a coupling reaction of alkynes with A-acylimines and A-acyliminium ions mediated by Cu(I) in water to generate propargyl amide derivatives.57 Either an activated imine derivative or imininum derivative was proposed as the intermediate, respectively. 

An indium chloride-catalyzed coupling of alkynes to aldehydes was also possible in giving a, (J>-unsaturatcd carbonyl compounds in water in low yields (Eq. 8.88).223 (Alkynylation is discussed in Chapter 4 on alkynes.)... 

The participation of complex substrates was illustrated in an elegant total synthesis of (-)-terpestacin (Scheme 8) [24,25]. Coupling of alkyne 12 and aldehyde 13 with Ni(COD)2, phosphine 14, and Et3B afforded product 15 as a 2.6 1 mixture of regioisomers, and a 2 1 diastereoselectivity in a combined 85% yield. Whereas alkynes that possess two aliphatic substituents generally... 

Zhao and Larock have described the synthesis of carbazoles, indoles, and dibenzofurans 118 via a Ic type cyclization that follows a sequence of Pd-catalyzed cross-coupling of alkynes and aryl iodides 116, then nitrogen-directed palladium migration to an arylpalladium intermediate 117 that undergoes an intramolecular Mizoroki-Heck ring closure <06JOC5340>. 

The inter- and intramolecular catalytic reductive couplings of alkynes and aldehydes recently have experienced rapid growth and are the topic of several recent reviews.5 h-8k 107 With respect to early transition metal catalysts, there exists a single example of the catalytic reductive cyclization of an acetylenic aldehyde, which involves the titanocene-catalyzed conversion of 77a to ethylidene cyclopentane 77b mediated by (EtO)3SiH.80 This process is restricted to terminally substituted alkyne partners (Scheme 53). 

For selected reviews encompassing intra- and intermolecular direct reductive coupling of alkynes to carbonyl partners, see [151-158]... 

The [Ir(cod)2]BARF complex also showed high catalytic activity in the hydrogena-tive coupling of alkyne with aldimines to lead to reductive couphng products, aUyl amines [69]. 

In this section I refer to a number of cycloadditions which cannot be categorized into the above-described types. For example, Murai and colleagues reported the four-component coupling of alkyne, hydrazone, hydrosilane and CO. Here, the [Ir4(CO)i2]-catalyzed reaction proceeded under pressurized CO conditions at high temperature, whereby a seven-membered nitrogen heterocycle was obtained (Scheme 11.37) [48]. 

Fagnola, M. C. Candiani, I. Visentin, G. Cabri, W. Zarini, F. Mongelli, N. Bedeschi, A. Solid-Phase Synthesis of Indoles Using the Palladium-Catalysed Coupling of Alkynes with Iodoaniline Derivatives, Tetrahedron Lett. 1997, 38, 2307-2310. 

There have also been several reports of the cyclization of diynes with amines under the influence of copper(I) chloride (equation 73) (65CB98, 70KGS125, 72TL3487). This is a potentially useful reaction for symmetrically substituted pyrroles, since symmetrical diynes can be obtained by oxidative coupling of alkynes. 

Unusual regioselectivity has been observed180 during the reductive coupling of alkynes and allenes by hydrozirconation and zinca-Claisen rearrangement. 

In 2002, the coupling of alkynes with nitrones catalyzed by Cu(I)/bis(aza-ferrocene) has been reported to produce (3-lactams enantioselectively [156]. The generation of... 

Patel and Jamison [40] reported a catalytic three-component coupling of alkynes, imines, and triethylborane using a Ni complex and (S)-(+)-(neomenthyl)diphenyl-phosphane [(S)-NMDPP] 159 forming the alkylative coupling product (Scheme 9.28). No yields were reported. 

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