Alkynyltin reagents

Successful extensions to sp-carbon cross-coupling reactions with vinyl triflates are exemplified by the synthesis of the etiyne 32 [Eq. (15)]. It is noteworthy that this reaction is compatible with the presence of alkynylsilanes, emphasizing the different behavior of organosilicone and organotin derivatives [25]. 

This protocol and the Pd-Cu-catalyzed direct cross-coupling with terminal acetylenes (Section 5.3.5) directly complement each other. The following examples, which cannot be applied to the latter, give normal coupling products only by Stille method [Eqs. 17-20] [28-31]. This method is especially useful for the cross-coupling reactions of organometallic complexes with cyclopentadienyl ligand that are sensitive to amines [Eq. 19] [30]. 

Finally, Pd(0) complexes can catalyze the coupling reaction between transition-metal halides 54 and tin acetylides 55 [Eq. (21)]. These reactions occui under the same reaction conditions, leading to the formation of carbon-carbon bonds in the presence of palladium catalysts [33]. 

Applications of this protocol to the synthesis of natural products are reported ever more frequently, undoubtedly because of the mild conditions needed and the complete chemoselectivity. Pd-catalyzed coupling with alkynylstannane 58 has been used to synthesize a key intermediate 59 of vitamin D metabolites [Eq. (22)] [331. Similar reactions 

The cross-coupling of organic electrophiles with organostannanes, commonly known as the Stille reaction, is one of the most versatile and selective palladium-catalyzed cross-coupling reactions [190]. Today, the Stille reaction is found among the routinely performed transformations in organic chemistry when it comes to 

In demanding cross ouplings, for instance, with electron-deficient alkynes, the Stille coupling frequently gives better results than the preparatively simpler Sonogashira reaction [200]. Furthermore, the neutral conditions of the Stille reaction mixture are particularly suitable for base-sensitive substrates that may otherwise decompose under the conditions used in the Sonogashira coupling. 

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Alkynyltin reagents applications, 9, 360 in Sonogashira coupling, 11, 18 in i/ -hydridized carbon polymerization, 11, 674-675 Alkynyltriphenylbismuthonium salts, in G—heteroatom bond formation, 9, 450... 

Z)-Tributylstannyl 3-iodoacrylates undergo Stille couplings with alkynyltin reagents to form (Z)-2-en 4-ynoic acid intermediates 642, which cyclize to yield either 5-methylenefuran-2(5//)-ones 643 or 2//-pyran-2-ones 644 (Scheme 149, Table 30). Factors that affect whether the pyranone or furanone cyclization predominates from this... 

Table 30 Products of the Stille coupling of (Z)-tributylstannyl 3-iodo-acrylates and alkynyltin reagents (Scheme 149)...

An example that used this protocol the substrate of which contains a sensitive functionality is depicted in Scheme 45 [202]. 1,3-Diene monoepoxide is easily attacked by a palladium(O) complex to form the corresponding 7r-allylpalladium species. Thus such a process could be banished from the desired selective transformation as depicted in Scheme 46 by the employment of the alkynyltin reagent with an aid of triphenylarsine ligand [203]. Organotin protocol is also convenient for introduction of a small alkynyl moiety such as C2 or C3 or preparation of symmetrical diarylethynes (Scheme 47) [204]. Shirakawa et al. reported recently that iminophosphine 4 is much more effective ligand for palladium than tris(2-furyl)phosphine in this reaction (Scheme 48) [32,205]. 

A particularly interesting application of this protocol, in conjunction with the direct cross-coupling with terminal acetylenes is shown in Scheme 5-2. Here, the first coupling occurs between the alkynyltin reagent 50 and the cyclized palladium intermediate 49 and is followed by the second direct coupling with the terminal acetylene 52 at the vinyl bromide moiety to yield unsymmetrical cyclic dienediyne 53 [32]. 

Table 9.16 Selection of recent Stille cross-couplings between organohalides and alkynyltin reagents.

The coupling between an electron-deficient and a strained olefin has been reported [184]. In the presence of in-situ-generated Ni(0)-catalyst, MesSiCl and an oxazoline ligand, the coupling of an enone with norbornene or norbomadiene and an alkynyltin reagent proceeds efficiently with the production of up to five stereocenters in a highly diastereoselective vision. 

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