Tetracyanoethylene reactions

The Dk parameter is based on the solvent effect, on the reaction of tetracyanoethylene with diazodiphenylmethane with benzene as a reference solvent. For details see Osbima, T. Arikata, S. Nagai, T. J. Chem. Research (S), 1981, 204... 

Endo adducts are usually favored by iateractions between the double bonds of the diene and the carbonyl groups of the dienophile. As was mentioned ia the section on alkylation, the reaction of pyrrole compounds and maleic anhydride results ia a substitution at the 2-position of the pyrrole ring (34,44). Thiophene [110-02-1] forms a cycloaddition adduct with maleic anhydride but only under severe pressures and around 100°C (45). Addition of electron-withdrawiag substituents about the double bond of maleic anhydride increases rates of cycloaddition. Both a-(carbomethoxy)maleic anhydride [69327-00-0] and a-(phenylsulfonyl) maleic anhydride [120789-76-6] react with 1,3-dienes, styrenes, and vinyl ethers much faster than tetracyanoethylene [670-54-2] (46). 

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

Tetracyanoethylene undergoes two principal types of reactions, addition to the double bond and replacement of a cyano group. Addition of hydrogen catalyzed by Pd gives 1,1,2,2,-tetracyanoethane [14778-29-1] (14). 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Unsaturated hydrazones, unsaturated diazonium salts or hydrazones of 2,3,5-triketones can be used as suitable precursors for the formation of pyridazines in this type of cyclization reaction. As shown in Scheme 61, pyridazines are obtainable in a single step by thermal cyclization of the tricyanohydrazone (139), prepared from cyanoacetone phenylhydrazone and tetracyanoethylene (76CB1787). Similarly, in an attempted Fischer indole synthesis the hydrazone of the cyano compound (140) was transformed into a pyridazine (Scheme 61)... 

Benzo[Z)]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z)]furan and 2- and 3-vinylindoles give adducts involving the exocyclic double bond. In contrast, the benzo[c]-fused heterocycles function as highly reactive dienes in [4 + 2] cycloaddition reactions. Thus benzo[c]furan, isoindole (benzo[c]pyrrole) and benzo[c]thiophene all yield Diels-Alder adducts (137) with maleic anhydride. Adducts of this type are used to characterize these unstable molecules and in a similar way benzo[c]selenophene, which polymerizes on attempted isolation, was characterized by formation of an adduct with tetracyanoethylene (76JA867). 

The reaction of o-diphenylcyclobutadiene (generated in situ by oxidation of its iron tricarbonyl complex) with p-benzoquinone yields A as the exclusive product. With tetracyanoethylene, however, B and C are formed in a 1 7 ratio. Discuss these results, and explain how they relate to the question of the square versus rectangular shape of cyclobutadiene. 

The azomethine imines exhibit the typical cycloaddition behavior expected of 1,3-dipolar species [fSJ] Numerous [3+2] cycloaddition reactions have been performed [201 204] Tetracyanoethylene adds to azomethine imines across the nitnle function instead of the C=C double bond This reaction is a rare example of this type of periselectivity [208] (equation 47)... 

Compare electrostatic potential maps for the following Diels-Alder transition states cyclopentadiene+ethene, cyclopentadiene+acrylonitrile and cyclopentadiene+ tetracyanoethylene, with those of reactants cyclopentadiene, ethene, acrylonitrile and tetracyanoethylene. Are electrons transferred from diene to dienophile in the transition states (relative to reactants) or vice versa For which reaction is the transfer the greatest The least Quantify your conclusion by measuring the total charge on the diene and dienophile components in the three transition states. 

Experimentally, the rates of Diels-Alder reactions between electron-rich dienes and electron-poor dienophiles generally increase with increased alkyl substitution on the diene. This is because alkyl groups act as electron donors and lead to buildup of electron density on the diene. An exception to this is the reaction of Z,Z-hexa-2,4-diene with tetracyanoethylene (TCNE), which is actually slower than the corresponding addition involving E-penta-1,3-diene. 

The ease with which 2,5-diamino-3,4-dicyanothiophene (67) is formed in 92% yield by saturating a solution of tetracyanoethylene in acetone-carbon disulfide with H2S is reminiscent of the aforementioned reactions/ "... 

Tetramethyl-l,2-oxathietane (138) was prepared by diazotization of 139, which was prepared from the aziridine (140) (86JA3811).Tlie reaction presumably involves the decomposition of the sulfonium ion intermediate (141).Tire dichloromethane solution of 138 at -20°C is sufficiently stable to permit exploration of the chemical reactions. Tire oxathietane 138 undergoes a formal [[Pg.248]

Reaction of l-methyl-4-oxo-6,7,8,9-tetrahydro-4//-pyrido[l, 2-n]pyrimi-din-l-ium-2-olate (148) with tetracyanoethylene afforded 3-substituted derivative 149 (95H(40)681). 

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. 

The comparison of rates of cycloaddition of maleic anhydride, tetracyanoethylene, and styrene to PPA shows that the latter, irrespective of the presence of electronegative groups, behaves in these reactions not as an electron-poor diene system. This fact, together with the composition of side products (giving evidence of PPA decarboxylation), allows the assumption to be made that the cycloaddition of dienophiles involves mainly decarboxylated polyene sections of cis-transoid structure213, 266. This is in agreement with the fact that PPA with predominant trans-transoid configuration interacts with these dienophiles at a substantially lower rate. The ultimate amounts of the dienophile combined with PPA of this structure is also considerably smaller. 

In another aspect of the mechanism, the effects of electron-donating and electron-withdrawing substituents (p. 1065) indicate that the diene is behaving as a nucleophile and the dienophile as an electrophile. However, this can be reversed. Perchlorocyclopentadiene reacts better with cyclopentene than with maleic anhydride and not at all with tetracyanoethylene, though the latter is normally the most reactive dienophile known. It is apparent, then, that this diene is the electrophile in its Diels-Alder reactions. Reactions of this type are said to proceed with inverse electron demand ... 

Alkenes with electron-withdrawing groups may form cyclobutanes with alkenes containing electron-donating groups. The enamine reactions, mentioned above, are examples of this, but it has also been accomplished with tetracyanoethylene and similar molecules, which give substituted cyclobutanes when treated with alkenes of the form C=C—A, where A may be... 

Alkenes of all types can be converted to cyclopropane derivatives by this reaction (though difficulty may be encountered with sterically hindered ones). Even tetracyanoethylene, which responds very poorly to electrophilic attack, gives cyclopropane derivatives with carbenes.Conjugated dienes give 1,2 addition ... 

---