Alkynyltins

Multinuclear ( H, 13C, nB) NMR spectroscopy is undoubtly the most useful and powerful method for the investigation of the organoboration of 1-alkynyltin, -germanium, and -silicon compounds allowing not only the structure of the final products to be determined but also the product ratio to be ascertained (Tables 6-8). 

The two acetylenic functions in the silicon or tin derivative make possible a competition between 1 1 and 2 1 reactions (Scheme 39, pathway b), and the product ratio depends significantly on the reaction conditions. For silicon derivatives an excess of 1-boraadamantane in the reaction mixture (acetylenic component added to 1-boraadamantane) leads to the octacyclic compounds 88 (up to 60%), while when the much more reactive 1-alkynyltin analogues are used, a second intramolecular 1,1-organoboration often takes place <2001CEJ775>. The stmcture of 88c (M = Sn, R = Me, R1 = SiMe3) was confirmed by X-ray analysis <2001CEJ775>. 

Alkynyltin and alkynyllead derivatives were extensively studied by PES, together with NMR and pseudopotential calculations88,92,93,97. For the sake of simplicity we will divide the compounds investigated into two classes ... 

Alkynyltin compounds also take part in Stille coupling reactions with alkyl, aryl, or acyl halides or triflates (e.g., Equation (89)).251 These reactions are covered in Volume 11. 

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)...

The regio- and stereoselective addition of alkynyltins to tin-substituted acetals produces propargylic ether derivatives (Equation (62)).216... 

Alkynyltins couple with 4-acetoxy-l,3-dioxane in the presence of BF3-OEt2 to give acetal protected propargylic anti- 1,3-diols (Equation (63)).217... 

The superior ability of alkynyltins to defer Pd-catalyzed alkynylation until after completion of the competing cyclic carbopalladation has been exploited in the synthesis of neocarzinostatin model compounds [85-87] (Scheme 28). 

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]. 

S.6.1. by Reaction of Alkynyltin Compound unit Transition- or Inner Transition-Metal-Carbonyl Complexes. 

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