Phenylacetylene acetylenes

CONDENSATIONS WITH SODAMIDE IN LIQUID AMMONIA Acetylenic compounds are conveniently prepared with the aid of Uquid ammcx as a solvent. The preparation of a simple acetylenic hydrocarbon ( -butylacetylene or 1-hexyne) and also of phenylacetylene is described. Experimental details are also given for two acetylenic carbinols, viz., 1-ethynyl-eyciohoxanul and 4-pentyn-l-ol. It will be noted that the scale is somewhat laige smaller quantities can readily be prepared by obvious modifications of the directions. 

Solutions of RC triple-bond C—Ti(0-/-C2H2)2 can be prepared by treating acetylenic compounds, such as phenylacetylene, with butyl lithium and then Cl—Ti(0-/-C2H2)2. These materials can react with aldehydes and epoxides to give the expected addition products (215). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

The additions of phenyl azide and phenylnitrile oxide to pentafluorophenyl-acetylene are also regiospecific [75, 7S] (equation 12). Interestingly, in the latter reaction, phenylacetylene gives regiochemistry that is opposite to that observed for pentafluorophenylacetylene [75]... 

Although hexafluoro-l,3-butadiene is better known for its [2+2] reactions, its Diels-Alder reactions, particularly with electron-deficient alkenes such as acrylonitrile and perfluoropropene, are not unknown [9] The first report of a Diels-Alder reaction is with an acetylenic dienophile Although the major product of Us reaction with phenylacetylene is its [2+2] adduct, a 3 5% yield of products of a Diels-Alder reaction is also observed [123] (equation 103)... 

Nonactivated terminal acetylenes have been added to enamines derived from aldehydes. A long reaction time or catalysis by copper(I) chloride is necessary. Thus the enamine (16) formed the adduct (72) on heating with phenylacetylene (64). 

From the two possible intermediates (a vinylacetylene, or a -chlorovinyl ketone as in Section II,C, 2,c) the latter would appear more probable the addition of benzojd chloride to phenylacetylene yielding 3-ehloro-3-phenylacrylophenone (/S-chlorochalcone) is not reported in the literature, however. Replacing the acetylene by Schiff bases or nitriles, azapyrylium or diazapyrylium can be obtained. 

The reactivity of arylhalides in the acetylenic condensation sharply decreases in the series Ar—I, Ar—Br, Ar—Cl. The rate of reaction of phenylacetylene with iodo derivatives is 800 times higher than that of the reaction with bromo derivatives and is 10 higher than that of the reaction with corresponding chlorides (75JOM253). Taking into account the very low activity of halogenopyrazoles (66AHC347), the catalytic variant of acetylenic condensation mainly involves the most active iodo derivatives. 

The copper-catalyzed 1 1 additions of aliphatic and aromatic sulfonyl chlorides82,85 or bromides84 to acetylenes yielding mixtures of trans- and cis-/3-halovinyl sulfones have also been described. Highly polar solvents favored trans addition, while cis addition predominated in low polarity media84,85. A comparison between the thermal and the copper-catalyzed addition of sulfonyl bromides to phenylacetylene (cf. Scheme 6) enabled Amiel84 to suggest that the two stereoisomers do not have a common intermediate. That is, the trans addition product is a result of a normal radical chain, while the cis addition... 

Although the reaction of certain acetylenes such as phenylacetylene and ethyl phenylpropiolate with cold concentrated sulfuric acid to give acetophenone (15) and benzoylacetic acid (16) has been known since the 1880 s, it was only in the 1960 s that this reaction was studied mechanistically. 

A more detailed study of the hydration of phenylacetylene, 9a, and three substituted phenylacetylenes, p-methoxy 10, p-methyl 11, and p-chlorophenyl-acetylene 12, in aqueous sulfuric acid containing 5% ethanol has been carried out by Noyce and co-workers (19,20). The hydration obeys general acid catalysis and gives a linear Hq dependence. The slopes for the logarithm of the observed rate constants versus Ho and the activation parameters for the hydration of these phenylacetylenes are summarized in Table II. 

Naumberg, Duong, and Gaudemer (729) have studied the stereochemistry of the addition of various acetylenes to [Co (DMG)2py] in methanol. They found, as already noted by Schrauzer and Windgassen 163), that the main product from the reaction with phenylacetylene in alkaline solution (pH > 10.5) was the jS-phenylvinyl complex (PhCH=CHCo), formed by the trans addition of the Co(I) anion and a proton, i.e.. 

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

Pd-catalyzed cross-coupling of aryl iodide 38 and terminal phenylacetylene 39 gave a dimer (e. g. 40) containing both trimethylsilyl-protected acetylene and aryltriazene moieties. 

Terminal acetylenes such as phenylacetylene are transformed by Znl2, CuCl, CuBr, or CuCN and BTSP 1949 into 1-iodo- 1976, 1-chloro- 1978, 1-bromo- 1979, or l-cyano-4-phenylaIkynes 1980 and to the diacetylene 1977 [156] (Scheme 12.44). 

Hydroxy(tosyloxy)iodobenzene 2014 reacts with phenyltrimethylsilane 81 in boiling acetonitrile to give diphenyliodonium tosylate 2015 and trimethylsilanol 4 or HMDSO 7 [184, 185]. Likewise, treatment of 2,5-bis(trimethylsilyl)furan 2016 with 2014 in boiling acetonitrile/methanol affords 78% iodonium tosylate 2017 and trimethylsilanol 4 [185]. In the presence of Bp3-OEt2 iodosobenzene oxidizes allyl-trimethylsilanes such as 2018 to unsaturated aldehydes such as 2019 in 63% yield, with formation of iodobenzene and trimethylsilanol 4 [186]. Analogously, vinyltrimethylsilanes such as (Z)-l-trimethylsilyl-2-phenylethylene 2020 afford, via 2021, acetylenes such as phenylacetylene in 61% yield and iodobenzene and trimethylsilanol 4 [187] (Scheme 12.54). 

Methanofullerene 20 with phenylacetylene dendrimer addends has also been reported [45] (Fig. 10). The UV absorption of fullerodendrimer 20 is particularly strong and is mainly attributed to transitions located on the two dendritic branches of the molecule. The photophysical investigations revealed that the large poly(aryl)acetylene branches act as photon antennae [46]. 

Fig. 2. A poly(phenylacetylene) dendrimer with an energy gradient across the conjugation length of the acetylene units from the periphery to the focal point...

Activated Acetylenes. The reaction of triphenylphosphine with phenylacetylene has been investigated in more detail.The rearrangement has been shown to proceed via the vinylphosphonium salt (30). 

In the thermal reaction of aliphatic and aromatic sulfonyl chlorides with acetylenes no adduct has been observed . However, the light-catalyzed additions of sulfonyl iodides to acetylenes as well as the thermal addition of sulfonyl bromides to phenylacetylene to form 1 1 adducts have been shown to be stereoselective and to occur in good to excellent yields. The fact that the addition occurs in a trans manner forced the authors to suggest that chain transfer by the sulfonyl halide (/cj) is much faster than isomerization of the intermediate vinyl radical (/c ) (see Scheme 5). 

---