From diaryl alkenes

Fischer, M. Wan, P. m-Quinone methides from m-hydroxy-1,1-diaryl alkenes via excited-state (formal) intramolecular proton transfer mediated by a water trimer. J. Am. Chem. Soc. 1998, 120, 2680-2681. 

In contrast, a Markovnikov addition of water was reported in the irradiation of a variety of o-hydroxystyrenes, again in aqueous acetonitrile, with the formation of 2-(2-hydroxyphenyl)ethanols. In this case, an intramolecular proton transfer from the excited state of the styrene was envisaged as the first step of the reaction [51]. A similar mechanism was postulated in the photohydratation of m-hydroxy-1,1 -diaryl alkenes that gave the corresponding 1,1-diarylethanols, although direct protonation of the P-carbon by water competed in some cases [52]. 

The photoinduced anti-Markovnikov addition of methanol to 1,1-diphenylethene reported by Arnold and co-workers in 1973 provides the first example of the addition of a nucleophile to an arylalkene radical cation. There are now a number of studies that demonstrate the generality of nucleophilic addition of alcohols, amines, and anions such as cyanide to aryl- and diaryl-alkene radical cations. Product studies and mechanistic work have established that addition occurs at the 3-position of I-aryl or 1,1 -diarylalkene radical cations to give arylmethyl or diaryl-methyl radical-derived products as shown in Scheme I for the addition of methanol to 1,1-diphenylethene. For neutral nucleophiles, such as alcohols and amines, radical formation requires prior deprotonation of the 1,3-distonic radical cation formed in the initial addition reaction. The final product usually results from reduction of the radical by the sensitizer radical anion to give an anion that is then protonated, although other radical... 

Wilcox et al. have demonstrated an application of the precipitation approach for MBH adduct isolation. By using a diaryl alkene alcohol (14) as a precipitating auxiliary (based on the solubility switch of structural isomerization), the corresponding MBH acids 17 were obtained from the reaction of acrylate 15 and aldehydes in the presence of DABCO, followed by isomerization and cleavage, in moderate to good yield (Scheme 2.11). 

Fragmentation Dominant a-cleavage to give the benzoyl ion, followed by decarbonylation to a phenyl ion of lower intensity. a-Cleavage in acetophenone also produces the acetyl cation (m/z 43). Even-mass maxima due to alkene elimination via McLafferty rearrangement. CO elimination from diaryl ketones through skeletal rearrangements. 

Selenium di-imides (132) were formed in methylene chloride solution from selenium tetrachloride with t-butylamine or sulphonamides and also from selenium metal with anhydrous Chloramine-T. They were found to be efficient reagents for the allylic amination of alken and alkynes. The first examples of selenium imides (133) were synthesized from diaryl selenides and Chloramine-T, from... 

Introduction of two different chalcogen elements to the C-C unsaturated bond is of particular interest from both synthetic and mechanistic viewpoints. Therefore, extensive studies have been carried out on the development of the (RE)2/(R E )2 binary system without using RE-E R compounds, which are difficult to prepare. (Z)-l-Seleno-2-thio-1-alkenes are produced regio- and stereoselectively when a mixture of diaryl disulfides and diaryl diselenides is subjected to a rhodium-catalyzed reaction with alkynes (Equation (68)).193... 

A study of debrominations of vtc-dibromides promoted by diaryl tellurides and din-hexyl telluride has established several key features of the elimination process the highly stereoselective reactions of e/7f/tro-dibromides are much more rapid than for fhreo-dibromides, to form trans- and cw-alkenes, respectively the reaction is accelerated in a more polar solvent, and by electron-donating substituents on the diaryl telluride or carbocation stabilizing substituents on the carbons bearing bromine. Alternative mechanistic interpretations of the reaction, which is of first-order dependence on both telluride and vtc-dibromide, have been considered. These have included involvement of TeAr2 in nucleophilic attack on carbon (with displacement of Br and formation of a telluronium intermediate), nucleophilic attack on bromine (concerted E2- k debromination) and abstraction of Br+ from an intermediate carbocation. These alternatives have been discounted in favour of a bromonium ion model (Scheme 9) in which the role of TeArs is to abstract Br+ in competition with reversal of the preequilibrium bromonium ion formation. The insensitivity of reaction rate to added LiBr suggests that the bromonium ion is tightly paired with Br. ... 

Diaryl-1,2,3,5-oxathiadiazines (277 from sulfur trioxide and aryl isocyanates) with (3-diketones yield pyrimidines (278). s-Triazine reacts with RCH2CN to give 4-aminopyrimidines (279 see Section 3.2.1.6.1 for a similar reaction), and with electron-rich alkenes and alkynes to yield pyrimidines such as (280) from EtC = CMe (Section 3.2.1.10.2). 

Diaryl butadienes 69 can be made by method 61b as the ylid from 68 is conjugated and will give one -alkene while the other comes from an aldol condensation used to make the enal.15 (chapter 19). 

The indium hydride compound, generated in situ from sodium borohydride and a catalytic amount of indium(m) chloride, selectively reduces carbon-carbon double bonds in conjugated alkenes such as a,a-dicyano olefins, a,/3-unsaturated nitriles, cyano esters, cyanophosphonates, diesters, and ketones (Scheme 107).372 This combined reagent system in acetonitrile reduces exclusively the a,/3-carbon-carbon double bond in a,/3,7,<5-unsaturated diaryl ketones, dicarboxylic esters, cyano esters, and dicyano compounds (Scheme 108).373... 

Nickel(O) triphenylphosphine species have been used to convert allyl halides to 1,5-hexadiene [332], for the reductive coupling of ethylene with aryl halides to give 1,1-diaryl-ethanes [333], and for the coupling of aryl halides and alkenes to prepare substituted olefins [334], In addition, l,2-bis[(di-2-propylphosphino)benzene]nickel(0) has been used for the reductive coupling of aryl halides [335], and l,2-bis[(diphenylphosphino)ethane]-nickel(O) has been employed to synthesize biphenyl from bromobenzene [336] and to prepare benzoic acid from bromobenzene in the presence of carbon dioxide [337]. 

Method C (general procedure). The vicinal dibromide (1-2 mmol) and the diaryl ditel-Inride (1-2 mmol) are reflnxed in tolnene or HOAc for 1-4 h (1,2-dibromoethane is used neat). After cooling, the mixture is filtered to remove the Te (quantitative yield) and the diaryltellurinm dibromide is precipitated by addition of hexane. The alkene is obtained by evaporation of the filtrate (cinnamic and fumaric acids, both insolnble in petrolenm ether, are separated from the tellurium dibromide with EtOH). 

In 2,9-diaryl-l,10-phenanthrolines (see Figures 7.10 and 7.20), bridgeheads and 1,10-phenanthroline unit are connected directly, leading to a rather stiff entity. The active centre, the copper ion bound to the nitrogen atoms of the 1,10-phenanthroline can only be reached from below through the bimacrocycle. In the cyclopropanation, the active species is a copper-carbenoid. When the alkene approaches it, the substituents of the alkene and the carboxylate of the carbenoid try to avoid sterical compression within the cavity and take up maximal distance to one another. Thus, the exo-product is formed with high selectivity. 

In the 1990s, Tingoli and coworkers developed a general approach to various arylselenated products by the reaction of unsaturated compounds with diaryl diselenides and (diacetoxyiodo)benzene [600-603]. Various phenylselenated products are formed in good yields from the reaction of alkenes with diphenyl diselenide and (diacetoxyiodo)benzene in acetonitrile. In particular, cyclohexene under these conditions stereoselectively affords fra i -l-acetoxy-2-(phenylseleno)cyclohexane (541) in good yield (Scheme 3.214) [603]. 

We look at these reactions in detail in Sections 11.3 and 6.6, respectively. For the moment we need only note that the p-C—H of these cyclic dialkyls is held away from the metal and so is not available for p elimination. The P C—C bond is held close to the metal, however, and so these rearrangements are really p eliminations involving a C—C, rather than a C—H, bond. The reaction of Eq. 3.21 is of particular significance because it is the key step of an important catalytic reaction, alkene metathesis, which converts propene to butene and ethylene (Chapter 11). The anion of [Li(tmeda)]2[(CH2)4-Pt(CH2)4] contains two tetramethylene rings bound to square planar Pt(II) and is thermally rather stable. Cyclic diaryls are rare an interesting and very stable example is shown below ... 

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