Diynes, intermolecular

Terminal alkynes undergo oxidative coupling in the presence of the GuGl-TMEDA catalytic system in [G4GiIm]PF6 under aerobic conditions to produce 1,3-diynes. " Intermolecular Pauson-Khand reactions of strained alkenes with alkynes and Go2(GO)g were performed in [G4GiIm]PF6 either thermally or in the presence of... 

Aryl- and alkenylcarbene complexes are known to react with alkynes through a [3C+2S+1C0] cycloaddition reaction to produce benzannulated compounds. This reaction, known as the Dotz reaction , is widely reviewed in Chap. Chromium-Templated Benzannulation Reactions , p. 123 of this book. However, simple alkyl-substituted carbene complexes react with excess of an alkyne (or with diynes) to produce a different benzannulated product which incorporates in its structure two molecules of the alkyne, a carbon monoxide ligand and the carbene carbon [128]. As referred to before, this [2S+2SH-1C+1C0] cycloaddition reaction can be carried out with diyne derivatives, showing these reactions give better yields than the corresponding intermolecular version (Scheme 80). 

The same type of bis-functionalization has been reported for the palladium-catalyzed borylstannylative carbocy-cyclization of 1,6-, 1,5-, 1,7-diynes, bis-propargylamine, and ether.377 It should be noted that even 1,2-dialkylidene cyclobutane can be obtained in reasonable yield. Ito has proposed the related silaborative reaction involving nickel(O) catalysis.378 This reaction has been performed in an intra- and intermolecular fashion. The intramolecular reaction allows the formation of cyclic dienes and the intermolecular process proceeds through a dimerization of alkynes to give acyclic dienes. 

In Section 9.2, intermolecular reactions of titanium—acetylene complexes with acetylenes, allenes, alkenes, and allylic compounds were discussed. This section describes the intramolecular coupling of bis-unsaturated compounds, including dienes, enynes, and diynes, as formulated in Eq. 9.49. As the titanium alkoxide is very inexpensive, the reactions in Eq. 9.49 represent one of the most economical methods for accomplishing the formation of metallacycles of this type [1,2]. Moreover, the titanium alkoxide based method enables several new synthetic transformations that are not viable by conventional metallocene-mediated methods. 

The Pd-catalyzed electro-cleavage of the C—O bond of allyl aryl ether proceeds smoothly in a DMF-Bu4NBp4-(Mg)-(Stainless Steel) system, giving depro-tected products in 73 99% yield [437]. The sp-sp intermolecular coupling reaction with the Pd water-soluble catalyst prepared in situ from Pd(II) acetate and sul-fonated triphenylphosphine in an MeCN-H2O system yields diynes in 45 65% yields [438]. Similarly, the sp -sp coupling of 2-iodophenols or 2-iodoanilines and terminal alkynes followed by intramolecular cyclization gives indol and furan... 

In the intermolecular reaction of tetraynes, where two 1,6-diyne moieties were directly connected, with monoalkynes, CHIRAPHOS (2,3-bis(diphenylphosphino) butane) was the choice of chiral ligand, and axial chirality was enantiomericaUy generated between the formed benzene rings (Scheme 11.17). Hexaynes with a 1,3-diyne moiety also underwent an intramolecular [2-i-2-i-2] cycloaddition, and the Ir-xylylBINAP (2,2 -bis[di(3,5-xylyl)phosphino]-l,l -binaphthyl) catalyst induced an excellent enantiomeric excess (ee) (Scheme 11.18) [24]. 

An intermolecular coupling reaction between three organonitrile molecules and a silicon-tethered diyne is reported to give good yields of pyrrolo[3,2-f]pyridine derivatives <2004JA7172>. The reaction is promoted by a low-valent zirconocene species (Equation 13). 

This type of intramolecular silylformylation is applicable to 4-silyloxy-l,6-diyne 176 which gives 177 in good yields (Equation (31)). The remaining alkynyl moiety in 177 can further undergo intermolecular silylformylation. " ... 

Pd/tppts-catalysed intermolecular sp-sp couplings to afford diynes and sp2-sp coupling of 2-iodophenols or iodoanilines with alkynes followed by intramolecular cyclization to benzofurans and indoles, respectively, with moderate to good yields in H20/CH3CN solvent mixtures have also been described.517 8... 

Diynes are also used to perform intermolecular enyne metathesis. With the objective of producing functionalized hetero- and carbocycles, a cascade diyne-alkene cross metathesis leading to five-membered cyclic products has recently been proposed [27] (Scheme 13). 

In a similar vein, cyclizations of diynes bearing propargyl carboxylates have been described to synthesize dienes and pyrones (equation 90). In the last case, a new cascade allows the intermolecular addition of electron-rich arenes. ... 

As is the case with totally intermolecular cocycloadditions, chemoselectivity is a potential problem in partially intramolecular systems where the desired process, combination of a diyne with a monoyne, may face competition from cycloadditions involving either exclusively the diyne or exclusively the monoyne. In practice chemoselectivity is readily achieved. Phosphite complexes of Ni° chemoselectively catalyze rapid and efficient cycloaddition of alkynes to heteroatom-containing diynes in good yields (equation... 

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. ... 

Polyynes have served as starting materials for the synthesis of a wide variety of heterocyclic ring systems. The reactions used involve addition to triple bonds, and any of the common mechanistic pathways may be followed, i.e. nucleophilic, electrophilic or free radical attack as well as concerted cycloadditions. Although the evidence does not permit unequivocal classification of many of the reactions into one of these categories, the ones considered here are those which most likely involve nucleophilic attack at some stage. In a formal sense the reactions amount to successive additions of a divalent nucleophile to two triple bonds the first involves intermolecular and the second intramolecular attack, as illustrated in equation (19) for the addition of HoS to a diyne. 

There are at least two issues to be addressed regarding the Type lie circular cascade process shown in Scheme 42. One is the regioselectivity in the initial intermolecular carbopalladation. Since it is not very difficult to differentiate the two terminal positions of cYj -diynes, this is not a serious problem in most cases. A more serious problem is the exclusive formation of fulvene derivatives observed in a couple of cases [124] (Scheme 45). It is not very clear what the scope of the fulvene formation is and whether the course of the reaction could be altered to give benzene derivatives. 

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... 

The regiochemical product distribution of the co-cyclization of two or three different alkynes occurs statistically. In some cases carefully controlled reaction conditions allow isolation of a main product from mixed cyclotrimerizations. For example, l,2,3,4-tetraphenyl-5,6-diethylbenzene can be obtained from cobalt-catalyzed reaction of tolane and 3-hexyne in good yield [62]. The first example of an intermolecular, regiospecific cross-benzannulation reaction catalyzed by Pd(PPh3)4 was reported by Yamamoto [63]. The reaction of 2-alky 1-but-l-ene-3-yne with disubstituted diynes leads exclusively in high yields to... 

Arenes from enynes and diynes. A novel synthesis of alkynylarenes by the intermolecular cycloaddition of enynes and diynes has been developed. With enynes alone the products are 2,6-disubstituted styrenes which are formed by cyclodimerization. Note that benzynes undergo trimerization to give triphenylenes in situ, e.g., by treatment of o-trimethylsilylphenyl triflate with CsF in the presence of (PhjPl.Pd. ... 

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