Dimerization ethylene derivative

Gyclobutane ring from ethylene derivatives Dimerization... 

In contrast to the reaction carried under an Ar atm, when (S)-49 was treated with 10 mol% la under an atmosphere of ethylene (22°C, CH2C12,24 h), (S)-41 was obtained in 81% isolated yield and >98% ee (Scheme 12). As expected, the use of ethylene atmosphere proved to be necessary for preferential monomer formation (10% of the derived dimer was also generated). These results indicate that the presence of ethylene is imperative for efficient metal-catalyzed chromene formation as well for processes involving disubstituted styrenyl ethers (25-30% yield of dimer 50 under argon). 

Considering the facility with which dimerization products 81 and 84 are obtained, we reasoned that, in catalytic ring closure of 77, the derived dimer is perhaps initially formed as well. If the metathesis process is reversible [17b], such adducts may subsequently be converted to the desired macrocycle 76. To examine the validity of this paradigm, diene 77 was dimerized (— 85) by treatment with Ru catalyst lb. When 85 was treated with 22 mol% 2 (after pretreatment with ethylene to ensure formation of the active complex), 50-55% conversion to macrolactam 76 was detected within 7 h by 400 MHz H NMR analysis (Eq. 8). When 76 was subjected to the same reaction conditions, <2% of any of the acyclic products was detected. Although we do not as yet have a positive proof that 85 is formed in cyclization of 77, this observation suggests that if dimerization were to occur, the material can be readily converted to the desired macrolactam, which is kinetically immune to cleavage. 

The relation is different when the initial reaction is followed by a virtually irreversible process. For example, reduction of 1,1-diphenyl-ethylene yields radical-anions which subsequently dimerize. The dimerization is virtually irreversible its rate constant was recently determined by the flash-photolysis technique82 and shown to vary from 1 x 108 for the Li+ salt to 30 x 108 M-1 s-1 for the Cs+ salt. The irreversibility of dimerization makes the conversion quantitative in spite of the relatively low electron affinity of the ethylene derivative. 

The polymerization of ethylene derivatives has recently become extremely important for the manufacture of plastics. Certain substituents in ethylene — those that increase the polarization — increase both the extent and the rate of polymerization. Such substituents are aromatic groups (as in styrene), oxygen-containing groups (as in acrolein, acrylic esters, and vinyl esters and ethers), and halogens (as in vinyl chloride). Multiplication of these substituents, however, depresses or completely suppresses the tendency to polymerize for instance, stilbene gives only a dimer when illuminated in benzene.14... 

Dimerization. The last problem to be discussed concerns the radical anions of 1,1-diphenylethene [(C6H5)2C = CH2], which will be denoted by D. These radical anions, like most radical anions of ethylene derivatives, undergo rapid dimerization to yield their respective dimeric dianions ... 

Lithium (s. a. under Cul) Reductive dimerization of ethylene derivatives with and without substitution... 

Manganese cobaltous chloride Reductive dimerization of ethylene derivatives... 

Carbon tetrabromide Oxidative dimerization of electron-ridi ethylene derivs. 

Potassium hexacyanoferrate(III) oxygen Oxidative dimerization to ethylene derivatives with decarboxylation... 

The paper describes the first asym. hydroboration with a chiral catalyst. E A soln. of norbornene and catalytic amounts of chloro(l,5-cyclooctadiene)rhodium(I) dimer and DIOP (2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) in THF flushed with argon, stirred at 20° for 15 min, cooled to —78°, 1.2 eqs. catecholborane added, stirred for 5 min, allowed to warm to —40°, maintained at this temp, for 72 h, recooled to —78°, ethanol, 3 M NaOH, and 30% H2O2 added, the mixture allowed to warm to 25° during ca. 1 h, then stirred for 12h cjco-(lR, 2R)-norborneol. Y 99% (e.e. 55%). The method is generally applicable (even to 1,1-disubst. ethylene derivs. ) and expensive chiral boron-reagents are not necessary. F.e.s. K. Burgess, M.J. Ohlmeyer, J. Org. Chem. 53, 5178-9 (1988) from allyl alcohol O-derivs. s. Tetrahedron Letters 30, 395-8 (1989). 

Dimerization and reductive dimerization of ethylene derivatives Cation specificity... 

Sodium tert-butoxide Ethylene derivatives from halides by dimerization... 

Autoxidation of organophosphorus compounds Ethylene derivatives by oxidative dimerization... 

A number of cases are known where ethylene derivatives undergo n cycloaddition to form cyclobutanes. Tetracycanoethylene [TCNE (NC)2C=C(CN)2] and fluorinated ethylenes are particularly prone to behave in this way. These reactions were discovered at the laboratories of duPont de Nemours Co. and have been studied in great detail by Bartlett and his collaborators. As we have already seen, concerted cis dimerizations of this kind should be less favorable than an path via an intermediate 1,4-butadiyl biradical all these reactions in fact take place in this way. An interesting example is the reaction of TCNE with bismethylenecyclobutene (230). The normal Diels-Alder reaction to form (231) is inhibited because this would be an antiaromatic cyclobutadiene derivative and because the transition state leading to it would be isoconjugate with benzocyclobutadiene. The product is therefore the spiran (232), formed as indicated by an process. 

Acetic acid/irradiation Cyclobutane ring by dimerization of ethylene derivs. 

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