Diphenylacetylene reduction

It should be noted that the selective reduction of phenylacetylene and diphenylacetylene to either the ds-alkene or the alkane was achieved using LiAlH4 in the presence of FeCk or NiCk as a catalyst [90, 91]. However, deuterolytic workup of the reaction mixtures gave deuterium incorporations <26%, indicating that these reagent systems are not well suited for the synthesis of vinyl- or alkylaluminum compounds from alkynes. 

Benzenecarhodithioesters and carbo-thio-S-esters were shown to yield diphenylacetylene by the cathodic reduction in aprotic media. Thus, the formation of diphenylacetylene involves [202] two molecules of a substrate. The cathodic reactivity of thioamides involving a similar alkylation of the C=S group in the presence of primary alkyl halides was reviewed [199-201]. 

The disodium salt of diphenylacetylene dianion is stable in THE solution at -78°C. Methanol acts as a proton source toward the salt and causes the formation of a mixture of 1,2-diphenylethane with diphenylacetylene and small amounts of tran -stilbene (Chang and Johnson 1965, 1966). It seems logical that the reaction between (PhC=CPh) , 2Na and MeOH leads at first to PhCH=CHPh. The second step is supposed to consist of the further reduction of PhCH=CHPh at the expense of electrons from the nonreactedpartof the initial dianion. In principle, the electron transfer may proceed faster than the reaction of the initial dianion with protons. As a result, the diphenylacetylene dianion has to discharge into diphenylacetylene, whereas stilbene dianion has to form diphenylethane as follows ... 

Other ring cleavages involve the reduction of the triazolotriazole (11), which gives 4-phenyltriazole, and the reaction of the mesoionic oxatriazolone (12) with diphenylacetylene, giving 1-cyclohexyl-4,5-diphenyltriazole, possibly through cyclohexyl azide as an intermediate... 

Reduction of diphenylacetylene with sodium in methanol or with zinc yielded stilbene, whilst reduction with sodium in ethanol gave 1,2-diphenyl-... 

Boger et al. reported the first total synthesis of ningaline D (282) starting from the diphenylacetylene 1092 and dimethyl l,2,3,4-tetrazine-3,6-dicarboxylate (1093) (687). In this synthesis, the key step is the formation of the fully substituted pyrrole core using an inverse electron demand heterocyclic azadiene Diels-Alder reaction followed by a reductive ring contraction of the resultant 1,2-diazine. 

One of the complexes formed in the reaction of diphenylacetylene and iron dodecacarbonyl is a red, crystalline compound of the composition [Fe2(CO)6(PhC2Ph)], which, on reduction with sodium in liquid ammonia, gives dibenzyl (117). By analogy with the cobalt carbonyl complex, structure (XXXV M = Fe) is proposed, in which the 7r-elcctrons of the triple... 

Dicyclopentadienyldinickeldiphenylbutadiyne-dicobalt hexacarbonyl has been prepared from diphenyldiacetylene in which one triple bond acts as a bridging group between two nickel atoms and the other between two cobalt atoms (203). Reduction of the diphenylacetylene complex (R = R = Ph) with sodium and alcohol in liquid ammonia yields dibenzyl, showing that the diphenylacetylene grouping is bonded only to the nickel atoms. The corresponding complex of acetylene (R = R = H) has also been prepared from nickeloccne and acetylene (69) ... 

Since the substitution reaction succeeded so well with olefins, the obvious extension to acetylenes was tried. Of course, only terminal acetylenes could be used if an acetylenic product was to be formed. This reaction has been found to occur but probably not by a mechanism analogous to the reaction of olefins (43,44). It was found that the more acidic acetylene phenylacetylene reacted with bromobenzene in the presence of triethylamine and a bisphos-phine-palladium complex to form diphenylacetylene, while the less acidic acetylene, 1-hexyne did not react appreciably under the same conditions. The reaction did occur when the more basic amine piperidine was used instead of triethylamine, however (43). Both reactions occur with sodium methoxide as the base (44). It therefore appears that the acetylide anion is reacting with the catalyst and that a reductive elimination of the disubstituted acetylene is... 

A polymer-supported lipoamide-ferrous chelate system was used as catalyst for the reduction of diphenylacetylene to cis-stilbene with sodium borohydride the dithiol-iron(II) (1 1) complex formed was suggested to be the active species. The chitosanlipoamide system has the highest activity among various insoluble polymers investigated 95,96). 

As regards the protecting effect, the complex is stable to Lewis acids. Also, no addition of BH3 occurs. As Co2(CO)6 can not coordinate to alkene bonds, selective protection of the triple bond in enyne 137 is possible, and hydroboration or diimide reduction of the double bond can be carried out without attacking the protected alkyne bond to give 138 and 139 [32], Although diphenylacetylene cannot be subjected to smooth Friedcl Crafts reaction on benzene rings, facile /7-acylation of the protected diphenylacetylene 140 can be carried out to give 141 [33], The deprotection can be effected easily by oxidation of coordinated low-valent Co to Co(III), which has no ability to coordinate to alkynes, with CAN, Fe(III) salts, amine /V-oxidc or iodine. 

Bis(triethylphosphine)platinum[l,8]naphthalene 56 undergoes diphenylacetylene insertion and reductive elimination to yield 1,2-diphenylacenaphthalene (Equation 18) <2005JA13494>. As noted in Equation (11), an analogous zirconacyclobutene complex inserts alkyne only upon prior transmetallation to nickel. 

PhC=CH and PhC=CPh analogs [Eq. (26)] (80). Five coordination is also found in the porphyrin alkyne complex, Mo(TTP)(PhC=CPh) (TTP= mesotetra-p-tolylporphyrin) (81). Reduction of a toluene solution of Mo(TTP)C12 with lithium aluminum hydride in the presence of excess diphenylacetylene produced the violet Mo(TPP)(PhC=CPh) adduct [Eq. (27)]. 

Nielson et al.292 have described the reduction of [WCl3L2(T)2-PhC2Ph)] (L = PMe3, PMe2Ph) under CO to afford the dichloro-diphenylacetylene complexes [WCl2(CO)L2(rj2-PhC2Ph)], which have both been characterized crystallographically. 

Zirconium(iv) benzamidinate [ PhC(NSiMe3)2 2ZrCl2] undergoes reductive coupling with diphenylacetylene in the presence of sodium amalgam to yield zirconacyclopentadiene 56 (R = = R = Ph) <1994OM4670,... 

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