Dichlorovinylene carbonate

New examples of [n2 +, 2] photocycloaddition of maleic anhydride (318) to alkenes have been reported.262 The major product of addition to ketene (319), for example, is the spiro cyclobutane (320).263 The stereoselective addition of dichlorovinylene carbonate to phenanthrene has been described,264 and the photoaddition of this carbonate (321) to the alkene (322)... 

Ortho photocycloaddition to benzene of derivatives of acetylene and maleimide proceeds via excitation of the alkyne or the maleimide. A few other alkenes follow the same route to ortho photocycloadducts among those are dichlorovinylene carbonate and some alkenes in which the double bond is conjugated with a cyano, carbonyl, or phenyl group, which makes it possible to excite them in the presence of the arene. 

Another reaction in which the excited alkene is the reactive species in ortho photocycloaddition is that of dichlorovinylene carbonate with benzene [82-84] (Scheme 15). 

This reaction proceeds only upon sensitization, preferably by acetophenone. The initial reaction is ortho addition of triplet excited dichlorovinylene carbonate to benzene, leading to endo and exo adducts. The exo isomer is quite stable and can be isolated, whereas the endo isomer is very sensitive to further reactions. The authors have considered the possibility of a stepwise reaction, but they prefer a formulation of the reaction mechanism in which an adiabatic reaction leads to triplet excited products. These decay to the ground-state ortho adducts or may... 

Scheme 15 Ortho photocycloaddition of benzene and dichlorovinylene carbonate.

In the addition of dichlorovinylene carbonate to isobutylene at low temperature, sensitized by acetone, the two-step nature has been illustrated [105], Thus, at — 20 °C a normal rc2 + tc2 adduct is formed. At lower temperature — 70 °C, a hydrogen transfer reaction competes with the cycloaddition to give the ene adduct ... 

Cyclobutanediones, once exotic compounds represented by a few perhalo derivatives, have become readily available as a result of new synthetic developments in recent years. These include the modified acyloin condensation 52) in which the intermediate enediolate is trapped as bis-trimethylsilyl ether (28) which can be converted to cyclobutanedione by reaction with bromine or hydrolyzed to acyloin and oxidized in a separate step. In addition to this efficient and general method, bi- or polycyclic unsaturated cyclobutanediones (30) have become available from photolysis of bridged cyclohexenediones (29) to be discussed in the following section. Photocycloaddition of dichlorovinylene carbonate (DCVC) to olefins53) promises to provide a third route if the problems associated with hydrolysis of the photoadducts (31) can be overcome. 

Furthermore, we studied the described dechlorination of tetrachloroethylene carbonate (V) to dichlorovinylene carbonate (VI) with zinc (Ref. 229). (VI) is an interesting intermediate which as a cyclophile permits simultaneous introduction of masked a-hydroxy keto and a-diketo functions respectively into the cycloadducts (Ref. 232). One example is given in scheme 180. 

The parent compound cyclobutane-1,2-dione itself was proposed as an intermediate in the acid- or base-catalyzed ring contraction of l,2-dichlorocyclobutyl-l,2-diylcarbonate (5), adduct of dichlorovinylene carbonate with ethene under photolysis, which on dissolution in cold dilute potassium hydroxide and subsequent acidification or on dissolution in hydrochloric acid, gave the 1-hydroxycyclopropanecarboxylic acid (6) as a single product. (For other examples of such a reaction, see ref 70.)... 

Diels-Alder dienophiles Dichlorovinylene carbonate. Dicyanoacetylene. Diethyl azodicar-boxylate. Dimethyl acetylenedicarboxylate. Ethylene, see 5,5-Dimethoxy-l,2,3,4-tetra-chlorocyclopentadiene. 4-Methyl-l,2,4-triazoline-3,5-dione. 4-Phenyl-l,2,4-triazoline-3,5-dione. 1,4-Phthalazinedione. 

Olefin additions Bromine azide. Bromine chloride. Bromine (chlorine) dipyridine nitrate. N-Bromoacetamine. N-Bromoacetamide-DMSO-Water. N-Bromoacetamide-Hydrogen fluoride. n-Butyllithium. Dichloroketene. Dichloromethyl 2-chloromethyl ether. N,N-Dichlorourethane. Dichlorovinylene carbonate. Difluoramine. Ethyl azidoformate. Ethyl bromoacetate. Iodine azide. Iodine isocyanate. Iodine nitrate, lodobenzene dichloride. 1-lodoheptafluoropropane. Mercuric acetate. Nitrosyl chloride. Nitrosyl fluoride. Nitryl iodide. Rhodium trichloride. Silver fluoride. 

Photochlorination z-Butylhypochlorite. Dichlorovinylene carbonate, see Lithium dicyclo-hexylamide. see Tetrahydrophthalazine. 

Photocyclization Chromyl acetate. Tetrachloro-cyclopentadienone ethylene ketal. Photocyclophile Dichlorovinylene carbonate. 

N,N-Dichlorourethane, 121-122 Dichlorovinylene carbonate, 122-123 a, -Dichloro-o-xylene, 399 Dicobalt octacarbonyl, 123 Di(cobalttetracarbonyl)zjnc, 123-124 Dicyanoacetylene, 21, 124-125... 

Cycloaddition l,l-Dichloro-2,2-difluoroethylene. Dichloroketene. Dichlorovinylene carbonate. N,N-Diethyl-l-propynylamine. Diphenylcarbodiimide. see Manganese dioxide, oxidation of dihydrobenzenes, see 4-PhenyI-l, 2,4-triazoline-3,5-dione. 

We attribute the observed inhibition to dichlorovinylene carbonate. There are good arguments for this assumption the photochlorination of ethylene carbonate is not restricted to monosubstitution, but it leads to a whole spectrum of chlorinated products. Separation by rectification is difficult since the chlorine-substituted derivatives of ethylene and vinylene carbonate show a marked anomaly of boiling points (I). One byproduct of the chlorination reaction is trichloroethylene carbonate which, in spite of careful distillation, remains in traces with the monochloro compound and is dehydrohalogenated in the second step of the synthesis to give dichlorovinylene carbonate. 

To test our assumption, we conducted polymerization experiments with small amounts of dichlorovinylene carbonate added to VCA. The inhibition effect was marked addition of even less than 0.5% dichlorovinylene carbonate completely suppressed radiation-induced polymerization of VCA under the given conditions. Although this may not be considered convincing proof, it is supported by the effect of reaction conditions on monomer quality the amount of trichloroethylene carbonate increases with more drastic chlorination condi-... 

Copolymerization of Vinylene Carbonate with Some Halo-Substituted Olefins. Copolymerization experiments were conducted using trans-dichloro-ethylene, vinylidene chloride, and CTFE since these monomers have a structural relation to the inhibiting impurities discussed above. With frans-dichloro-ethylene, no polymerization occurred, and only oligomers of VCA with a molecular weight of 300 were formed. Like dichlorovinylene carbonate, trans-dichloroethylene acts as an inhibitor, probably through degradative chain transfer by abstraction of a chlorine atom. 

DIKETONES r-Batoxybis(dimethylamino)mcthane. Dichlorovinylene carbonate. 

Figure 19 summarizes the work of Harper, who took the Diels and Adler adduct of dichlorovinylene carbonate with... 

Figure 19 Route from a dichlorovinylene carbonate-derived monomer.

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