Of aryl alkynes

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

Iodophenyl acetates undergo palladium-catalyzed carbonylation in the presence of aryl alkynes to yield flavones (Equation 309) <20000L1765>. 2-Iodophenols can similarly undergo a palladium-catalyzed carbonylation in the presence of terminal alkynes to afford chromones (Equation 310) <2005JOC6097>. 

Conditions based on stoichiometric amounts of silver oxide have been developed by Mori et al. for the synthesis of arylated alkynes from terminal alkynes and aryl iodides. Under such conditions, neither silylated alkynes nor aryl bromides or triflates did not undergo coupling (Scheme 10.78).129,130... 

Intramolecular solvomercuration of aryl alkynes (if. 11, 320). The triple bond of alkynylbenzenes substituted at the oz/Zio-position with suitable groups undergoes intramolecular acetoxymercuration with Hg(OAc), in HOAc to afford aromatic heterocycles such as benzofuranes, benzothiophenes, and chmmones. 

Alkylation of aryl -alkynes These alkynes undergo rapid alkylation with alkyl iodides in the presence of powdered KOH and a catalytic amount of 18-crown-6 (C6H6, 80°) yields 60-75%. 

Performing the reduction of the dichloride under an argon rather than dinitrogen atmosphere affords a phosphorus-bridged dizirconium complex where the bridging phenyl groups are reduced to bis(allyl) anions (341, Scheme 56).205 Addition of aryl alkynes to 338 offers another method of dinitrogen functionalization,... 

The Pd-catalyzed coupling of 2-halo-, and 2,6-dihaloquinoxalines (217) with propargyl alcohol was reported [110]. This process worked well for the simple alkyl-, and a range of aryl-alkynes, resulting in the corresponding 2-substituted quinoxalines. 

Arylalkynes. The above reaction has been extended to a synthesis of aryl alkynes by cross-coupling of a 1-alkynylzinc chloride with an aryl iodide or bromide (equation I) with tetrakis(triphenylphosphine)palladium(0) as catalyst. This method was used for the synthesis of l-(2 -thienyl)-l-propyne (1), which on... 

This process is commonly known as the Sonogashira reaction and has proven extraordinarily useful for the synthesis of a wide variety of aryl alkynes or enynes. When neighboring functionality exists, Pd and Cu salts are well known to effect cyclization to the corresponding hetero- or carbocycle. Thus, the reaction of terminal alkynes and aryl or vinylic halides bearing neighboring functionality often leads directly to heterocycles or carbocycles, providing a particularly useful synthesis of benzofurans and indoles. 

Imines derived from o-iodobenzaldehydes and o-iodoaniline have been utilized in the annulation of aryl alkynes to produce isoindolo[2,1-a]indoles (Eq.58) [119,120]. 

After optimization of the procedure, we have been able to employ a wide range of aryl alkynes and aryl halides in this process. This reaction involves a novel Pd migration from a vinylic position to an aryl position and subsequent ring closure (Eq. 87). 

Additional Hydrosilylations. Hydrosilylations of terminal alkynes with triethylsilane (eq 1) have been improved in terms of their regio- and stereocontrol as well as in other aspects of their operation. Through the employment of Pt(DVDS), Pt-catalyzed hydrosilylations of 1-alkynes can now be performed at room temperature and in water with very high selectivity for the ( )-/3-vinylsilanes (eq 20). It has also been shown that Pt02 catalyzes the internal hydrosilylation of aryl alkynes under orthosubstituent regiocontrol (eq Strong preference for the... 

Isoquinohnes were prepared by a rhodium-catalyzed annulation of pic-ohnamides with alkynes. A number of aryl alkynes are tolerated in this reaction (Scheme 52).With an asymmetric alkyne, the larger group (phenyl) is found distal to the amide. When the alkynes have alkyl groups instead of aryl, the yield is lowered.While some variation is also tolerated on the pico-linamide, when groups are placed at C-5, the yield is lowered, presumably due to steric hindrance (14SL1036). 

The dirhodium tetra(triphenylacetate) (Rh2TPA4)-catalyzed decomposition of ethyl 2-diazo-3-phenylpropanoate in the presence of aryl alkynes yields the angularly substituted dihydroazulenes 115. The formation of 115 presumably takes place by a tandem alkyne insertion/Buchner ring expansion pathway via intermediates 112-114. The reactivity of aryl alkynes with 2-diazo-3-phenylpropanoate is altered dramatically by changing the catalyst from dirhodium tetra(triphenylacetate) to dirhodium tetrapivalate (Rh2Piv4) cyclopropenes 116 are formed in 40-75% yields. 

Reduction of aryl alkynes provided styrene derivatives (Scheme When the hydroxy group in 21 was protected with a l-BuMe2Si group, the use of Pd/BaS04 as the catalyst gave even better yield of the cis product. 

For highly-substituted benzene derivatives, it is sometimes more efficient to build the aromaticring. Rich G. Carter of Oregon State University, in the cotirse of a synthesis J. Org. Chem. 2007, 72,9857) of siamenol 30, developed the Diels-Alder addition of aryl alkynes such as 27 to enol derivatives such as 28 to give the biphenyl 29. 

Wettergren et al. (2003) have studied in situ deprotection and co-methoxylation of TMS-protected aryl alkynes under microwave exposure. They found that using microwave technology, rapid co-methoxylation of aryl alkynes was possible. 

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