Dicyanoacetylene1

[1071-98-3]  · C4N2  · Dicyanoacetylene  · (MW 76.06)

(nucleophilic addition;4,5 [4 + 2] cycloaddition reactions;2 metal complexes insertion reactions3)

Physical Data: bp 76.5 °C; mp 20.5 °C; d 0.9703 g cm-3; IR 2268 cm-1 (w), 2212 cm-1 (m).

Solubility: sol all organic liquids.

Form Supplied in: clear colorless liquid.

Preparative Methods: see eq 1.

Purification: by simple vacuum sublimation or atmospheric distillation.

Handling, Storage, and Precautions: the solid compound can be stored indefinitely at dry-ice temperatures and is handled at rt. It is much more sensitive to the presence of oxygen, a polymerization or condensation reaction probably taking place.

Nucleophilic Addition.

Dicyanoacetylene is very susceptible to nucleophilic addition reactions. Thus it reacts at or below rt with ammonia and primary and secondary amines. The stereochemical aspects of this reaction have been investigated in the case of the piperidine and only the product of cis addition could be detected (eq 2).4 Preference for cis stereochemistry has also been observed in the addition reaction of methanol and isopropyl alcohol. t-Butyl alcohol gives an equal mixture of both isomers (eq 3).5

Dicyanoacetylene also reacts readily with hydrogen halides and halogens. They add to dicyanoacetylene at rt to give halodicyanoethylenes of unspecified stereochemistry. Addition of bromine to dicyanoacetylene affords the trans adduct in 57% yield (eq 4).6

[4 + 2] Cycloaddition.

Because of the nature of the electron deficiency of the p-system of dicyanoacetylene, it is a more active dienophile than any other activated alkyne including hexafluoro-2-butyne and acetylenedicarboxylate esters. It has the added advantage over the latter of being thermally more stable, and any excess is readily removed due to its low boiling point. Although no direct comparison has been made, it seems likely that dicyanoacetylene is also more reactive in most Diels-Alder reactions than Maleic Anhydride and Tetracyanoethylene; in fact it is probably only surpassed by benzyne, and some of the cyclic azo compounds. It reacts with cyclopentadiene, 1,3-cyclohexadiene, and butadiene at or below rt7 and adds, albeit with decreasing ease, to anthracene, naphthalene, and even benzene itself. The latter addition requires heating at 180 °C for extended periods and the yields are low. However, the reaction can be catalyzed with Aluminum Chloride and Aluminum Bromide. High yields of the adduct are obtained at rt; small amounts of phenylmaleo- and phenylfumaronitrile, the products of a Friedel-Crafts addition of dicyanoacetylene to benzene, are also isolated (eqs 5 and 6).

Dicyanoacetylene reacts with styrenes by sequential Diels-Alder addition and ene reaction to give adducts as illustrated (eq 7).8 The intermediate adduct from a 1:1 molar ratio of starting materials could not be isolated. The reaction again occurs under exceptionally mild conditions.

Dicyanoacetylene reacts at rt with quadricyclane (eq 8)9 and norbornadiene (eq 9)10 in good yields. With bicyclo[2.1.0]pentane it undergoes both a cycloaddition and an ene reaction (eq 10).11

Other examples of the high reactivity of dicyanoacetylene in the Diels-Alder reaction are its additions to furan and furan derivatives,12 fulvenes,13 1,4-diphenylnaphthalene,14 cyclooctatetraene,15 and [2.2]paracyclophane.16 Dicyanoacetylene acts as a 1,3-dipolarophile in reactions with diazomethane,17 ethyl diazoacetate,18 and benzonitrile oxide.19

In more recent studies, dicyanoacetylene was reacted with more complicated systems. It can react with linear fused aromatic and heteroaromatic compounds with good regioselectivity. The example shows its reaction with anthra[2,3-b]thiophene in refluxing toluene to give an 82% yield of cycloaddition adduct (eq 11).20

Under promoted conditions, dicyanoacetylene reacts with syn-o,o-dibenzene derivatives at rt to give domino- and pincer-type products. This specific reaction gives exclusive domino-type product; in some other cases the ratio could be lower (eq 12).21

Vinylcycloheptatriene derivatives also undergo Diels-Alder reactions with dicyanoacetylene exclusively via the cycloheptatriene form to give 68-96% yields of adducts (eq 13).22

With excess of cyclopentadiene, anti-sesquinorbornene can be made through the Diels-Alder reaction with dicyanoacetylene in good yield (eq 14).23

Reactions of antiaromatic compounds such as cyclobutadiene and azete with dicyanoacetylene yields Dewar benzene and 1-Dewar pyridine derivatives in fairly good yields. They can be converted by irradiation to benzene and pyridine intermediates (eqs 15 and 16).24

Dicyanoacetylene also serves as an important starting material in the synthesis of 1H-cyclopropa[l]phenanthrene (eq 17).25

Treatment of a solution of [22](1,4)cyclophane in CH2Cl2 with dicyanoacetylene in the presence of AlCl3 afforded 15,16-dicyano[22](1,6)cyclooctatetraenyl(1,4)cyclophane in 33% yield (eq 18).26

Radical Reaction with [1.1.1]Propellane.

The reaction of [1.1.1]propellane with dicyanoacetylene in chloroform proceeds extremely rapidly. It involves initial attack of the alkene under the flap of the bicyclopentane to produce a biradical intermediate which leads to the final product (eq 19).27

Cyclosubstitution Reaction.

On heating in toluene, 4,4-disubstituted 1,3-thiazole-5(4H)-thiones and dicyanoacetylene undergo a cyclosubstitution reaction to yield 2-methylidene-1,3-dithiol derivatives in 63% yield (eq 20).28

The regioselectivity of the cycloaddition of tetrasulfur tetranitride to dicyanoacetylene has been shown to favor 2,4-addition across nitrogen, or 1,5-addition across sulfur (eq 21).29

Photolysis.

Cycloaddition reactions of dicyanoacetylene with different alkenes not only can be initiated by heating and Lewis acids, but also can be promoted by photolysis. Subjected to UV radiation with ethylene, it forms 2,3-dicyano-1,3-butadiene at 254 nm (eq 22) or 1,2-dicyano-1-cyclobutene at 185 nm (eq 23).30

Metal Complex Insertion Reactions.

Insertion of alkynes into transition metal-hydride bonds is a key step in many important catalytic processes such as hydrogenation or polymerization. It also receives considerable attention by virtue of its utility in organic synthesis. Many transition metal complexes of Groups 6-10 play an important role in alkyne dimerization, oligomerization, and polymerization reactions, and in the formation of organometallic complexes that may be precursors for these reactions.31 It was thus of interest to study the reactions of cyanoalkynes towards these metals (Zr, Nb, Mo, W, Re, Fe, Co, Ni). The following are just a few examples of metal complexes with dicyanoacetylene (eqs 24-26).32-34

Related Reagents.

1,2-Dicyanocyclobutene; Dimethyl Acetylenedicarboxylate; Maleic Anhydride; Tetracyanoethylene.


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Feng Xu & James S. Panek

Boston University, MA, USA



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