1- Aryl-2- ethynes

Bromoquinoline (70), behaving similarly to a simple carbocyclic aryl bromide, was coupled with phenylethyne 121 to provide disubstituted ethyne 122 in 50% yield (2001JCS(P1)978). 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

In the direct synthesis of aryl terminal alkynes via Pd-catalyzed cross-coupling of aryl halides with ethynylmetals, formation of diarylethynes is one of the potential side reactions. Indeed, the Kumada coupling of 2-iodo-5-methylthiophene (29) with ethynylmagnesium chloride gave the desired 2-ethynyl-5-methylthiophene (30) in only 35% yield, along with 24% of bis(5-methyl-2-thienyl)ethyne (31) [29], The high propensity for H-Mg exchange reaction to occur was blamed for the diarylethyne formation. 

Despite the undeniable synthetic value of the benzannulation reaction of aryl and alkenyl Fischer carbene complexes, the details of its mechanism at the molecular level remain to be ascertained. Indeed, although a relatively large number of theoretical studies have been directed to the study of the molecular and electronic structure of Fischer carbene complexes [22], few studies have been devoted to the analysis of the reaction mechanisms of processes involving this kind of complexes [23-30]. The aim of this work is to present a summary of our theoretical research on the reaction mechanism of the Dotz reaction between ethyne and vinyl-substituted hydroxycarbene species to yield p-hydroxyphenol. 

The benzannulation reaction tolerates a range of alkyl and aryl allcynes, which may bear additional functionalities. The simultaneous presence of two bulky substituents directly attached to the C=C bond, as for example in bis(trimethylsilyl)ethyne, however, blocks the final electrocyclization and causes the reaction to stop at the vinyl ketene stage [44]. Neither very electron-rich nor very electron-poor allcynes can undergo benzannulation. Strongly electron-deficient allcynes such as hexafluorobut-2-yne cannot adequately compete with car-... 

The aryl vinyl tellurium compounds formed in these reactions (p. 401) are obtained exclusively, or at least predominantly, as the (Z)-isomers. With ethynyl ketones, aldehydes, acids, and esters, the nucleophile attacks the ethyne carbon in the / -position to the carbonyl groups Benzenetellurolate and bis[phenylethynyl] ketone produced only bis[2-phenyl-2-phenyltelluroethynyl] ketone and no monoadduct. ... 

Double couplings have been reported by Cummins [143] [bis(tributylstannyl)ethyne with aryl iodides], Tamao et al. [144] [tris(butylstannyl)phenylethyne with a dibromosilacyclo-pentadiene] and Diederich and co-workers [145] [tiis(butylstannyl)phenylethyne with an E-dibromoalkene]. Li et al. have obtained a bis(binaphthol) from a monoiodobinaphthol and bis(tributylstannyl)ethyne [146] in a yield of 66% (Scheme 4-42). 

Carbonylation. Insertion of CO into a C-S bond, and formation of lactams from unsaturated amines as well as indanones from l-aryl-2-(trimethylsi-lyl)ethynes" are realized in the presence of [Rh(cod)Cl]2. 

The Stille coupling between aryl halides and bis(tributylstannyl)ethyne furnishes symmetrical tolanes. Dienyl triflones are available in three steps from l-alkynes, with the reaction sequence terminated by a Stille coupling. 

Two groups have reported syntheses of the chiral o-diphenylphosphino-oxazolines (55) which involve the displacement of fluorine from the related o-fluorophenyloxazolines using potassium diphenylphosphide. High yields of o-substituted arylphosphines, e.g., (56), have been obtained in a similar manner from the reactions of o-substituted aryl fluorides with potassium diphenylphosphide. Displacement of chlorine from a chloroarene by potassium diphenylphosphide in liquid ammonia is a key step in the synthesis of the phosphinobiaryl (57). The reaction of potassium diphenylphosphide with 1,2-bis(diphenylphosphino)ethyne generates the salt (58), treatment of which with chlorodiphenylphosphine gives the tetrakis(diphenyl-... 

Scheme 7.17. Examples of the Stephens-Castro coupling reaction. In reaction (a), coupling between an aryl iodide (iodobenzene) and the organometallic (copper) alkyne [copper(p-methylphenyl)ethyne] produces the diarylacetylene. In reaction (b), the same process, this time starting with a vinyliodide (iodoethene), generates a vinylacetylene [4-(p-methylphenyl)-l-buten-3-yne],...

Scheme 7.18. Examples of the Sonogashira coupling reaction. In reaction (a), an aryl halide (X = Br, I) is coupled to the terminus of the (p-methylphenyl)ethyne. In reaction (b)> coupling is to a haloethene, prodncmg a substituted vrnylacetylene derivative. In both cases, catalytic (not stoichiometric) qnantities of palladium and copper catalysts are used.

The leacdons of the alkynides M(OGni)3 (M = Pr, Sm, Tb) with esters results in additum to the ester u> fixm alkoxy complmKes of the type M[OC(GECPhX(W )R ]3 (R R alkyl). Exce ethyne reacts widi various scandium cmnplexes Qp 2 (R - H, alkyl, aryl, allmnyl, alkynyl, amide) to form reacts with excess ethyne to fcmn polyacetylene. The ctxnplex... 

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