Terminal diynes

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

Terminal diynes could not be cleanly monoliydrozirconated it was necessary to protect one of the two acetylenic forms with EtMgBr/TMSCl to get single addition [85]. 

The rhodium-catalyzed cyclization/hydrosilylation of internal diyne proceeds efficiently with high stereoselectivity (Scheme 106). However, terminal diynes show low reactivity to rhodium cationic complexes. Tolerance of functionalities seems to be equivalent between the rhodium and platinum catalysts. The bulkiness of the hydrosilane used is very important for the regioselectivity of the rhodium-catalyzed cyclization/hydrosilylation. For example, less-hindered dimethylethylsilane gives disilylated diene without cyclization (resulting in the double hydrosilylation of the two alkynes), and /-butyldimethylsilane leads to the formation of cyclotrimerization compound. 

Oxidative Addition of Terminal Diynes to Electron-Deficient Metal Centers... 

In addition to their role as a source of lithiated diynes or terminal diynes silyl-protected diynes have found direct application in the preparation of Group 8 diynyl complexes. Reactions of Me3SiC=CC=CR (R = Ph, C=CPh, C=CC=CPh) with RuCl(PPh3)2Cp in the presence of KF afford the corresponding poly-ynyl complexes Ru(C=CC=CR)(PPh3)2Cp." ... 

A few mercury complexes featuring diynyl ligands are known. Deprotonation of W =C(NMe2)C=CC=CH (CO)s with BuLi, followed by treatment with HgCl2 has afforded Hg C=CC=CC(NMe2)=W(CO)5 2 and mercury(I) derivatives of more common terminal diynes HC=CC CR (R = Me, Ph) have also been described. ... 

The first tt complexes of 1,3-diynes were reported by Greenfield. Shortly thereafter, Tilney-Bassett described the first heterometallic derivatives. This area has grown steadily since these initial reports and many complexes of this type are now known. Diyne complexes are often simply alkyne-substituted analogues of conventional jr-alkyne complexes. Indeed, transition metal compounds that form -complexes with mono-alkynes can be expected to form complexes with diynes. However, the thermal sensitivity of terminal diynes, especially 1,3-butadiyne, may limit the application of routine reaction conditions in some cases. Further coordination of the ynyl ligand by additional metal fragments is usually determined by the reagent stoichiometry and by steric effects. 

As 1,2-disubstituted triple bonds do not generally react with allylic organozinc reagents, conjugated terminal diynes underwent chemoselective allylzincation at the terminal alkyne moiety leading to allyl-substituted conjugated enynes (equation 138)173. 

Helicene-based SPM (M,M,M)-120, as well as all other possible stereoisomers, have been synthesized by Yamaguchi and coworkers using a Sonogashira reaction of the corresponding diiodide and terminal diyne (Figure 6.6) [92], Self-aggregation of these SPMs was evident in concentration dependence 1H NMR spectroscopic studies inCDCl3 (0.1 and 10 mM). Dimer formation (even in benzene) was observed... 

We have studied homopolycyclotrimerizations of aliphatic terminal diynes with various alkylene spacer lengths catalyzed by tantalum and niobium halides or by binary mixtures of the metal halides and tetraphenyltin (Scheme 18) [64-66]. Under optimized conditions, completely soluble diyne homopolymers with high molecular weights (Mw up to 1.4 x 106) and pre-... 

Ni/IPr serves as a general catalyst system for the coupling of diynes and CO2. To date, this catalyst does not provide pyrones from either terminal diynes or sterically hindered diynes. Terminal diynes oligomerized at a faster rate than C02 incorporation. In contrast, sterically hindered diynes (R = f-Bu or TMS) did not react under any reaction conditions (elevated temperature and pressure). 

The increased reactivity of isocyanates, relative to carbon dioxide, was reflected in the wider range of cycloaddition partners. For example, terminal diynes as well as nontethered alkynes (e.g., 3-hexyne) were also successfully converted to 2-pyridones rather than undergoing rapid telomerization to aromatic by-products. Importantly, the cycloaddition of an asymmetrical... 

Introduction of two or more terminal diyne units, either at a metal center or, for example, on an q-ring-metal complex, gives the possibility of generating metal-based polymers. In the case of alkynes, many examples of polymers have been described, but studies of similar systems derived from di- or poly-ynes are in their infancy.90 Two- and three-dimensional polymers can be constructed in similar fashion, extension leading (conceptually, at least) to the formation of novel carbon allotropes. 

An intramolecular version of this process has been described, leading to bicyclic 2-pyrones. Diynes in which both alkyne functions are internal and are linked by three-, four- or five-atom chains cycloadd to carbon dioxide in the presence of catalytic Ni° and various trialkylphosphines (equation 51). Terminal diynes require stoichiometric metal and give lower yields, however. Extensive studies of ligand effects on yield and chemoselectivity have established a broad scope for the process and pointed out important practical differences between it and the intermolecular reactions described above. ... 

Allenediynes are obtained from the coupling of allenic bromides with terminal diynes . Thus from the bromide 53 and butadiynyl(trimethyl)silane (13) in the presence of copper(i) bromide and tri-/i-butylamine, the silylated derivative 54 was obtained in 70% yield. Removal of the silyl group by treatment with dilute methanolic alkali for 10 s afforded the free allenediyne 55 in 84% yield. 

Figure 7. Synthetic strategy to obtain a [3]catenate by cyclodimerization of a difunctional precursor. The circles represent the templating transition metal, and the triangles the terminal diynes.

Z-tamoxifen 403 tandem cyclization 290, 295 tandem Heck reaction-anion capture 253-4 tandem Heck reaction-phenoxide capture 253 tandem Heck reactions 251, 252-4 tandem intramolecular Heck-intermolecular Stille cross-coupling 255 taxol 140, 143,243,245 ( )-tazettine 146,234 telomerization 352 telomerization products 343, 345 template effect 140 teraconic anhydride 468 terminal acetylenes, synthesis of 216-20 terminal alkynes 6, 213 terminal 2,2-diorgano-l-aIkcnylboronates 51 terminal diynes 207 ternary complex 444 ternary coupling 177... 

A general and convenient route to conjugated diynes, especially terminal diynes from the corresponding chloroenynes, has been developed [21]. Thus, readily available ( )-iodochloroethylene was first reacted with alkynylzinc derivatives in the presence of a Pd-phosphine complex catalyst to produce ( )-chloroenynes 30 in high yield., The chloroenynes 30 could then be readily converted into the corresponding terminal diynes 31 [Eq.(12)]. 

Cycloaddition. Formation of [a,e]-fused cyclooctatetraenes by cyclodimerization of terminal diynes in a formal [2+2+2+2]cycloaddition is effected by (dme)NiBr2-Zn. ... 

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