Alkynylation arenes

After this work, the more challenging synthesis of arene-alkynylated indoles was investigated. Because of the enhanced reactivity of the pyrrole ring, the direct functionalization of indoles on the benzene ring is highly challenging. A domino process to access these compounds would therefore be very useful. They were able... 

Scheme 33 Domino cyclization-alkynylation for the synthesis of arene-alkynylated indoles...

At present, the chemisty of selenophenes and tellurophenes is a relatively scantily studied area. Nevertheless, a number of new valuable contributions dealing with their chemistry have emerged. Electrophilic cyclization of l-(l-alkynyl)-2-(methylseleno)arenes provides a route to a variety of 2,3-disubstituted benzo[fe]selenophenes, as illustrated by the preparation of the system 88. Other useful electrophiles for similar reactions are E or NBS <06JOC2307>. Similar chemistry has also been employed in preparation of 2,3-disubstituted benzo[f>]selenophenes on solid phase <06JCC163>. In addition, syntheses of 2,3-dihydroselenolo[2,3- >]pyridines have been achieved using radical chemistry <06OBC466>. 

The tantalum(V) calix[4]arene complex 44 provides an interesting scaffold for the construction of an j -PhC2C=CPh ligand upon reaction with an excess of phenylethynyllithium (Scheme 10). The coupling reaction is presumed to proceed via bis-alkynyl 45, which is subsequently attacked at the a-carbon of one of the acetylide ligands to give anion 46, isolated as its lithium salt. The addition of a further equivalent of LiC CPh is probably prohibited by orbital constraints. ... 

Arene-solvated cobalt atoms (U) and (1, obtained by reacting Co vapor and arenes, have been found by Italian workers to promote the conversion of a,d)-dialkynes and nitriles to alkynyl-substituted pyridines [87JOM(326)C33] (Scheme 4). 

The Pd-catalyzed alkynylation is one of the most widely used —C bond formation reactions. It has been thoroughly and extensively reviewed recently15-17. So only a brief overview and a discussion of some of the most recent advances will be presented in this section. As in the case of alkenyl-alkenyl coupling, Ni catalysts have rarely been used for alkynylation, even though Ni catalysts do affect the desired alkynylation in some cases. One main reason for disfavoring Ni is that Ni can readily react with alkynes to undergo alkyne cyclooligomerization represented by arene formation. The Pd-catalyzed alkynylation can, in principle, be performed in three discrete manners, as shown in Scheme 40. 

Support-bound triazenes, which can be prepared from resin-bound secondary aliphatic amines and aromatic diazonium salts [455], undergo cleavage upon treatment with acids, leading to regeneration of the aromatic diazonium salts. In cross-linked polystyrene, these decompose to yield nitrogen and, preferentially, radical-derived products. If the acidolysis of polystyrene-bound triazenes is conducted in the presence of hydrogen-atom donors (e.g. THF), unsubstituted arenes can be obtained (Entries 8 and 9, Table 3.47). In the presence of alkenes or alkynes and Pd(OAc)2, the initially formed diazonium salts undergo Heck reaction to yield vinylated or alkynylated arenes (Entry 10, Table 3.47). Similarly, unsubstituted arenes can be obtained by oxida-... 

Aluminum-alkynyl covalent bonds, characteristics, 9, 249-250 Aluminum-aluminum bonds in A1(I) compounds, 9, 261 in Al(II) compounds, 9, 260 Aluminum aryloxides, reactivity, 9, 254—255 Aluminum(III)ates, in organic group-selective transfers, 9, 279 Aluminum(I)-boron bonds, characteristics, 9, 263 Aluminum(III)-boron exchange, process, 9, 266 Aluminum-calix[4]arene catalyst, for alternating epoxide-CC>2 co-polymerization, 11, 617... 

Lactones, via indium compounds, 9, 686 Lactonizations, via ruthenium catalysts, 10, 160 Ladder polysilanes, preparation and properties, 3, 639 Lanthanacarboranes, synthesis, 3, 249 Lanthanide complexes with alkenyls, 4, 17 with alkyls, 4, 7 with alkynyls, 4, 17 with allyls, 4, 19 with arenes, 4, 119, 4, 118 and aromatic C-F bond activation, 1, 738 bis(Cp ), 4, 73... 

An expedient method for synthesis of 2,3-disubstituted 1-benzoselenophenes (91) by the electrophilic cyclization of various 1 -(1 -alkynyl)-2-(methylseleno)arenes (90) has been reported recently (Scheme 24). This method tolerates a wide of variety of functional groups, and proceeds under exceptionally mild reaction conditions [141], Moreover, an efficient solid phase synthesis of 91 based on a combination of palladium-mediated coupling and iodocyclization protocols has been developed [142],... 

Sodium thiophenoxide and bis phenyliodonium acetylene triflate afforded cleanly l,2-bis(phenylthio)acetylene [6]. Alkynyl iodonium salts have alkynylated several arene sulphonates which were converted into alkynyl aryl sulphones. The process is probably the best among other methods, as far as yield, availability of starting materials, non-toxicity and ease of handling are concerned. 

The synthesis of the first alkynyliodonium tosylates was achieved by the treatment of terminal alkynes with [hydroxy(tosyloxy)iodo]benzene (HTIB) (equation 8)8,10,11. Such reactions are generally conducted with an excess of alkyne in chloroform at reflux, although they can be carried out at room temperature, and dichloromethane can be employed as solvent. This procedure is, however, restricted to terminal alkynes in which R is either an aryl group or a bulky alkyl group. With linear alkyl groups (i.e. R = n-Pr, n-Bu, fl-C5Hn), phenyl(/ -tosyloxyvinyl)iodonium tosylates are obtained instead (equation 9)8. In some cases (R = /-Pr, /-Bu), mixtures of alkynyl- and (/ -tosyloxyvinyl)iodonium tosylates are produced8. ter -Butylacetylene appears to be the optimum substrate for this approach and has been employed with a series of [hydroxy(tosyloxy)iodo]arenes for the synthesis of various aryl(ter/-butylethynyl)iodonium tosylates (equation 10)9. 

A more general and efficient approach to alkynyl carboxylates, also thought to involve alkynyliodonium carboxylate intermediates, entails the treatment of bis(acyloxyiodo)-arenes with alkynyllithium reagents (equation 88)81. These reactions are best conducted in the presence of 2-nitroso-2-methylpropane in order to suppress oxidative coupling of the lithium acetylides by the acyloxyiodanes. 

The following phenol synthesis from easily accessible furyl alkynyl starting material was the first gold-catalysed reaction to proceed via car-benes and arene oxides (Ts = p-toluene sulfonate Cat = AUCI3 in... 

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