1,1-dicyanoethylenes

A study [19] of the cycloaddition between substituted (E)-l-phenyl-1,3-butadienes 55 and substituted 1,1-dicyanoethylenes 56 leading to cis- and trans-cyclohexenes 57 and 58 (Equation 5.8) has shown that diastereoselectivity is markedly dependent on pressure. 

In many cases, homopolymerization can be initiated by the anion-radicals of the monomers themselves. Of course, such monomers must have pronounced electron affinity (EA) and be stabilized by delocalization of an unpaired electron. Typical examples are represented by the anion-radicals of 1,1-dicyanoethylene (EA = 1.36 eV) and methyl or ethyl 2-cyanoacrylates (EA = 1.08 eV). In all of these anion-radicals, an unpaired electron is primarily localized on C atom of the CH2 segment and characterized by appreciable resonance stabilization (Brinkmann et al. 2002). These anion-radicals are nucleophilic and attack the neutral monomers to initiate polymerization. 

Another way of testing how one end of the dienophile affects the other end is to load up the dienophile with up to four electron-withdrawing groups, and see how each additional group affects the rate. A stepwise reaction between butadiene and tetracyanoethylene ought not to take place much more than statistically faster than a similar reaction with 1,1 -dicyanoethylene, but a concerted reaction ought to, and does, take place much faster. 

For the [2 + 2] cycloaddition of hydroxyethylene to 1,1-dicyanoethylene the intermediate exists in a very shallow potential well and has largely diradical, but some zwitterionic, character the charge transfer amounts to 0.2 electrons. The overall transition state for the reaction, which is the transition state... 

The [2 + 2] adduct from propenylidenecyclopropane and TCNE undergoes a cycloreversion at 1(X) °C to give 1,1-dicyanoethylene the solvent effect on this reaction is quite modest, a result not readily interpretable in terms of a zwitterionic transition state. ... 

In 1964, J. Sauer et al.43 reported the reactivity of cyclopentadiene (26) with the cyanoethylene series in the DA reaction (see Scheme 1 and Table 3). An analysis of the relative rates shows that the rate increases with the cyano substitution on ethylene. However, it is easy to see that the successive substitution on the Cl and C2 carbon atoms has a different incidence. For instance, while 1,1-dicyanoethylene (6) reacts more than 10.000 times faster than acrylonitrile (12), cis and trans 1,2-dicyanoethylene (37 and 38) are only ca. 100 times faster. In addition, tetracyanoethylene (2), the most reactive dienophile within the series, reacts only 100 times faster than tricyanoethylene (36) (see Table 3). These results indicate that the symmetric substitution at the Cl and C2 carbon atom of ethylene produces a loss of effectiveness of the EW effect of the substitution. 

The catalysts found active in the norbornadiene dimerization are various nickel tt complexes, among them Ni(CO)4, Ni(CH2=CHCN)2, Ni(0) complexes of 1,1-dicyanoethylenes, and the corresponding phosphine substitution or addition compounds (3, 32, 33, 47). Other active catalysts are Co2(CO)8, Fe2(CO)9, Co2(CO)g 2P(CgH5)3, Co(CO)3NO, and Fe(CO)2(NO)2 (3, 4, 32, 33, 44, 48). Efficient catalysts were also obtained by the in situ reduction of Ni, Co, or Fe chelates with organo-aluminum compounds (46, 49). Finally, dimerization of norbornadiene could also be effected with Rh on carbon (45). The nickel catalysts... 

Vinylidene cyanide (VCN), methyl vinylidene cyanide (MVCN), and 2-(2,4-difiuorophenyl)-1,1-dicyanoethylene (TSE) are noncommercially available monomers. 

The addition of 1,1-dicyanoethylenes to tetra-alkoxyethylenes gives cyclobutanes (43) Treatment of (43) with sodium methoxide results in the elimination of a molecule of hydrogen cyanide to give the cyclobutene (44), which may be hydrolysed to the cyclobutene-1,2-dione (45) or thermally rearranged to the 1,1,4,4-tetra-alkoxybutadiene (46). 

Duran and Bertran [4] studied by means of the MINDO/3 method possible mechanisms of the reaction of 1,1-dicyanoethylene with oxyethylene which may lead to two different products, i.e., l-oxy-3,3-dicyanocyclobutane XII and l-oxy-2,2-dicyanocyclobutane XIII ... 

Shinji Y, Emiko O (2008) An unusual reaction of a pyridinium yUde with 1,1-dicyanoethylene derivatives. Chem Lett 6 628-629... 

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