1,1-Diphenylethylene, addition

DiphenyhnethyUithium [881-42-5] can be prepared by the metalation reaction of butyUithium with diphenyknethane in addition, the adduct of butyUithium and 1,1-diphenylethylene is convenientiy prepared in either hydrocarbon or polar solvents such as THF as shown in equation 18. 

The necessary vicinal dihalides are themselves readily available by addition of Br2 or Cl2 to alkenes. Thus, the overall halogenation/dehvdrohalogenation sequence makes it possible to go from an alkene to an alkyne. for example, diphenylethylene is converted into diphenylacetylene by reaction with Br2 and subsequent base treatment. 

Dimsyl anion 88 is known to add to styrene, and to 1,1-diphenylethylene in the presence of a base, forming 3-arylpropyl methyl sulfoxides121. Treatment of ( )-3,3-dimethyl thiacyclo-oct-4-ene-l-oxide 89 with n-BuLi gave exo-4,4-dimethyl-2-thiacyclo-[3.3.0]octane 2-oxide 90, a bicyclic addition product of the internal double bond. A similar cyclization was observed in the reaction of 91 with n-BuLi122. 

Two pieces of direct evidence support the manifestly plausible view that these polymerizations are propagated through the action of car-bonium ion centers. Eley and Richards have shown that triphenyl-methyl chloride is a catalyst for the polymerization of vinyl ethers in m-cresol, in which the catalyst ionizes to yield the triphenylcarbonium ion (C6H5)3C+. Secondly, A. G. Evans and Hamann showed that l,l -diphenylethylene develops an absorption band at 4340 A in the presence of boron trifluoride (and adventitious moisture) or of stannic chloride and hydrogen chloride. This band is characteristic of both the triphenylcarbonium ion and the diphenylmethylcarbonium ion. While similar observations on polymerizable monomers are precluded by intervention of polymerization before a sufficient concentration may be reached, similar ions should certainly be expected to form under the same conditions in styrene, and in certain other monomers also. In analogy with free radical polymerizations, the essential chain-propagating step may therefore be assumed to consist in the addition of monomer to a carbonium ion... 

Diphenylethylene has been reported to add to several olefins/61 The cross-addition of this olefin with isobutene yields (41) in 63% yield ... 

It is well known that the kinetic effects of several substituents on one or two aromatic rings are not additive. This is exemplified in the bromination of 1,1-diphenylethylenes, stilbenes and a-methylstilbenes. The presence of a substituent, particularly one capable of electron donation by resonance, on the aromatic ring so alters the charge distribution at the transition state that the second substituent in the other ring then interacts with a charge different from that which would prevail if the substituent were alone. This is expressed... 

While we know of no experimental thermochemical data for 123, Roth informs us that the enthalpy of formation of 124 is 259 kJmol-1. There are no experimental thermochemical data for 125 either, but it is easy to estimate the desired enthalpy of formation. We may either use the standard olefin approach with ethylene, 1,3-butadiene and (E)-l,3,5-hexatriene (i.e. with CH2=CH2, 33 and 79) or linearly extrapolate these three unsaturated hydrocarbons. From either of these approaches, we find a value of ca 225 kJ mol-1. Cross-conjugation costs some 35 kJ mol-1 in the current case. Interestingly, the directly measured cross-conjugated 1,1-diphenylethylene (126) is only ca 10 kJmol-1 less stable than its directly measured conjugated (E)- 1,2-isomer (40) despite the expected strain effects that would additionally destabilize the former species. 

It is noteworthy that the nature of the ionic intermediate formed in bromine addition to olefins and the solvent properties also govern the competition between nucleophilic trapping and elimination. Thus 1,1-diphenylethylene, 11, gives the corresponding dibromide 13 (or solvent incorporated products, 14) and vinyl bromide, 12, in a ratio changing from 99 1 to 5 95 depending on solvent and on bromine concentration.(20) (see Table III results)... 

Analogously, bromine bridging is not the only factor affecting the elimination-nucleophilic trapping ratio. Pre-association with a nucleophilic solvent can explain the increased selectivity towards addition products with respect to elimination products, as observed in bromination of 1,1-diphenylethylene in methanol. 

Some readers may regret that we have taken our title so literally that we have not included the rate-constants of dimerisation, e.g., for diphenylethylene nor those for initiation by preformed cations (except marginally) nor the rate-constants for the addition of aryl and di-aryl cations to alkenes, established so elegantly by Wang and Dorfman (1980) and by Mayr and his collaborators (Mayr, 1990 Bartl et al., 1991 and numerous earlier papers). In our view these subjects are sufficiently interesting and important to be reviewed together in their own right. 

Already, at an early stage of the studies on the captodative effect, Viehe s group (Lahousse et ai, 1984) measured relative rates for the addition of t-butoxyl radicals to 4,4 -disubstituted 1,1-diphenylethylenes and to substituted styrenes. This study did not reveal a special character of captodative-substituted olefins in such reactions. It might be that the stability of the radical to be formed does not influence the early transition state of the addition step. The rationalization of the kinetic studies mentioned above in terms of the FMO model indicates, indeed, an early transition state for these reactions, with the consequence that product properties should not influence the reactivity noticeably. 

Photolysis of 21d (see earlier 21) in alkenes (cyclohexene, 1,1-diphenylethylene) always gave the cyclopropane derivatives 75 by a cis addition of the singlet carbene (64JOC3577) (Scheme 21). 

The optical density of w-BuLi shows good hnear behavior at 285 nm (e = 91 4 L moR cm ), in benzene solution, in the concentration range from 0.002 to 0.031 M. The weak absorption maximum in this region shifts slightly to a longer wavelength on increasing the concentration. The kinetics of n-BuLi addition to 1,1-diphenylethylene... 

The bromide-lithium exchange of l,l-dibromo-2,2-diphenylethylene (88) was thoroughly examined by Maercker and coworkers. It could be shown that the number of side-products drastically decreases when LiDBB instead of metallic lithium is used as lithiation agent. The reaction was performed in THF at low temperatures by addition of the solution of the geminal dibrominated aUcene to the solution of LiDBB (Scheme 32). By this method, l,l-dilithio-2,2-diphenylethylene (89) could be obtained in 36% yield together with the 1,4-dilithium compound 48 and monolithiated 47 (51 and 2%, respectively). The yields were determined after trapping the reaction mixture with dimethyl sulphate. 

The general characteristics of anionic copolymerization are very similar to those of cationic copolymerization. There is a tendency toward ideal behavior in most anionic copolymerizations. Steric effects give rise to an alternating tendency for certain comonomer pairs. Thus the styrene-p-methylstyrene pair shows ideal behavior with t = 5.3, fy = 0.18, r fy = 0.95, while the styrene-a-methylstyrene pair shows a tendency toward alternation with t — 35, r% = 0.003, i ii 2 — 0.11 [Bhattacharyya et al., 1963 Shima et al., 1962]. The steric effect of the additional substituent in the a-position hinders the addition of a-methylstyrene to a-methylstyrene anion. The tendency toward alternation is essentially complete in the copolymerizations of the sterically hindered monomers 1,1-diphenylethylene and trans-, 2-diphe-nylethylene with 1,3-butadiene, isoprene, and 2,3-dimethyl-l,3-butadiene [Yuki et al., 1964]. 

Annelation of additional aromatic units to the basic cis-1,2-diphenylethylene system exerts strong effects on its inherent reactivity. In the usual MO description these effects can be traced to the effect of the structure of the new skeleton on the highest occupied and lowest unoccupied orbitals at the atoms forming the new bond and therefore can be properly considered as topological effects. As such effects are quite numerous we shall limit ourseivs to only a few examples. Thus o-terphenyl 103) does not give any DHP under usual conditions ... 

In addition to its interesting structure, the triethylsilylium-aromatic complex has proved useful in preparing other cations. Reaction with 1,1-diphenylethylene, for example, provided the cation 95, the first example of a persistent p-silyl substituted carbocation (i.e., where decomposition by loss of the silyl group did not occur). 

The structure-reactivity behavior found for similar organosodium polymerization initiators of styrene [27] or that for addition reactions with 1,1-diphenylethylene [28] is almost identical with that found for the lithium initiators of Table 3.1. It is interesting to note from Table 3.1 that the reactivity of lithium... 

Surprisingly it was reported that when potassium cyanate is substituted for sodium cyanate the yields of carbamates are reduced to less than 5 %. The reason for this drastic effect is not known at this time. In addition, the use of other alkali or alkaline metal cyanates in this reaction has not been investigated. The Loev [28] procedure appears applicable to the synthesis of carbamates from primary, secondary, and tertiary alcohols (2 hr reaction time affords 60-90% yields), cyclic and acyclic 1,3-diols, phenols, oximes, ald-oximes, and ketoximes, and primary, secondary, and tertiary mercaptans. Carbamates could not be obtained from diphenylethylcarbinol (dehydrated to 1,1-diphenylethylene) or trichloro- and trifluoromethylcarbinols. 

On the other hand, It sometimes happens that the nucleo-philicity of the end standing precursor carbanlon has to be decreased to prevent side reactions. An easy way to achieve that is an Intermediate addition of 1,l-diphenylethylene." This procedure Is used especially when the second monomer to be added Is a methacryllc ester, to prevent attack of the ester carbonyl. 

Addition to alkenes can be sensitized by both electron-donors and electron-acceptors, and it is most likely that the reactive species is the alkene radical anion or the alkene radical cation, respectively. 1,1-Diphenylethylene can be converted to the Markownikov addition product with methanol (2.48) using the electron-donating sensitizer t-methoxynaphthalene no added proton acid is needed. Using... 

This has been studied much less frequently and appears to be a rather more complex reaction. The first results obtained, for the butyl-lithium, styrene reaction in benzene have already been described. In a similar way the addition of butyllithium to 1,1-diphenylethylene shows identical kinetic behaviour in benzene (26). Even the proton extraction reaction with fluorene shows the typical one-sixth order in butyllithium (27). It appears therefore that in benzene solution at least, lithium alkyls react via a small equilibrium concentration of unassociated alkyl. This will of course not be true for reactions with polar molecules for reasons which will be apparent later. No definite information can be obtained on the dissociation process. It is possible that the hexamer dissociates completely on removal of one molecule or that a whole series of penta-mers, tetramers etc. exist in equilibrium. As long as equilibrium is maintained, the hexamer is the major species present and only monomeric butyllithium is reactive, the reaction order will be one-sixth. A plausible... 

With diphenylhexyllithium 121) (the product of addition of butyl-lithium to 1,1-diphenylethylene) kinetic results are the same as found for fluorenyllithium initiation in the presence of moderate amounts of ether. Even in pure toluene, the rates are first order with respect to initiator concentration and monomer concentration. This simple behaviour is caused by a constant fraction of the initiator forming low molecular weight polymer. If butyllithium is used as initiator, the kinetic behaviour is too complex for analysis. 

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