Markovnikov reactions styrene addition

In the presence of peroxides, hydrogen bromide adds to the double bond of styrene with a regioselectivity opposite to Markovnikov s nrle. The reaction is a free-radical addition, and the regiochemistiy is governed by preferential fonnation of the more stable radical. 

In the phosphonium salt synthesis, the addition reaction of tertiary phosphines to activated alkenes has been reported (Scheme 3). PPh3 is added to electron-deficient alkenes such as enones or enals at the p-position in the presence of acids.4 The reaction of styrenes with phosphine has recently been reported by Okuma, which gave Markovnikov adducts.5 Although no catalyzed reactions of... 

Hosokawa, Murahashi, and coworkers demonstrated the ability of Pd" to catalyze the oxidative conjugate addition of amide and carbamate nucleophiles to electron-deficient alkenes (Eq. 42) [177]. Approximately 10 years later, Stahl and coworkers discovered that Pd-catalyzed oxidative amination of styrene proceeds with either Markovnikov or anti-Markovnikov regioselectivity. The preferred isomer is dictated by the presence or absence of a Bronsted base (e.g., triethylamine or acetate), respectively (Scheme 12) [178,179]. Both of these reaction classes employ O2 as the stoichiometric oxidant, but optimal conditions include a copper cocatalyst. More recently, Stahl and coworkers found that the oxidative amination of unactivated alkyl olefins proceeds most effectively in the absence of a copper cocatalyst (Eq. 43) [180]. In the presence of 5mol% CUCI2, significant alkene amination is observed, but the product consists of a complicated isomeric mixture arising from migration of the double bond into thermodynamically more stable internal positions. 

The reaction w ith styrene in acetonitrile, on the other hand, gives two vicinal fluoro sulfates 4 and 5 with preference for mn/ -Markovnikov regioselectivity, and svn addition with other alkenes.11... 

Iron salts (e.g. FeCls) have been identified as new catalysts for intramolecular hydroamination. A number of olefinic tosylamides underwent the reaction at 80 °C to form the corresponding the N-tosylpyrrolidine derivatives in good yield.63 The same salt can also catalyse Markovnikov addition of electron-rich arenes and heteroarenes to styrenes, giving rise to 1,1-diarylalkanes at 80 °C.64... 

A highly efficient inter- and intra-molecular addition of l,3-diketones//3-keto esters to styrenes (ArCH=CH2) has been developed. Silver triflate was identified as the most efficient catalyst (10 mol%). The reaction, affording formally the Markovnikov products, is reversible through the cleavage of a carbon-carbon bond by silver at an elevated temperature.70... 

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]. 

As demonstrated below, a Lewis acid-mediated reaction was utilized in the synthesis of dihydro[b furan-based chromen-2-one derivatives from l-cyclopropyl-2-arylethanones and allenic esters <070L4017>. The TiCh-catalyzed anti-Markovnikov hydration of alkynes, followed by a copper-catalyzed O-arylation was applied to the synthesis of 2-substituted benzo[6]furan <07JOC6149>. In addition, benzo[6]furan-based heterocycles could be made from chloromethylcoumarins <07SL1951>, substituted cyclopropanes <07AGE1726>, as well as benzyne and styrene oxide <07SL1308>. On the other hand, DBU-mediated dehydroiodination of 2-iodomethyl-2,3-dihydrobenzo[6]furans was also useful in the synthesis of 2-methylbenzo[Z>]furans <07TL6628>. 

Diethyl N,A -dibromophosphoramidate undergoes ready Markovnikov addition to styrene or cyclohexene (92%) in ecu at -20 to -t-20 C with BF3-Et20 catalysis.Alternatively, such reactions can be carri out in refluxing CH2CI2 in the absence of catalyst, when anti-Markovnikov products (47-97%) are formed. All these compounds are versatile intermediates (Scheme 83). A few N-bromoperfluo-roamines have been added to alkenes, thermally or photolytically. ... 

Products of addition to styrene double bonds can arise as a result of light induced electron transfer reactions. Lewis has studied the intramolecular reaction of l-phenyl-w-amino alkenes (422) 289,290 products arise from electron transfer from the amine nitrogen to the excited state of the styryl group followed by intramolecular proton transfer in the radical ion pair produced. The resultant biradical then couples to yield the isolated products (423) and (424). Sensitisation of the intermolecular analogue of this reaction by 1,4-dicyanobenzene has been reported and is proposed to occur by electron transfer from the styrene to the excited state of the sensitiser followed by attack of an amine on the styrene radical cation. This ultimately leads to the product of anti-Markovnikov addition of the amine across the double bond of the styrene. This is similar to the sequence long since established by... 

Reaction of DCT with styrene in polar protic solvents (water, acetic acid, and methanol) proceeds with the electrophilic addition of the halogen and the solvent moieties according to the Markovnikov rule. In carbon tetrachloride in the presence of an initiator (AIBN) addition of DCT and TBT to styrene proceeds to form anti-Markovnikov adducts and a small amount of 1,2-dihalo derivatives (69ZC325) (Scheme 72). 

As noted above the anti-Markovnikov addition of alcohols to alkenes has attracted considerable mechanistic and synthetic interest. Absolute rate constants for the reaction of alcohols with styrene radical cations have been measured and representative data are summarized in Tables 3 and 5. In this case the high oxidation potentials of simple alcohols effectively rule out the possibility of electron transfer as a competing reaction. Furthermore, transients assigned to the benzyl radical produced by... 

The Wacker reaction has been applied to numerous simple olefins such as a-olefins and cycloalkenes, or to functionalized olefins such nitroethylene, acrylonitrile, styrene, allyl alcohol, or maleic acid [3]. The carbonyl group is formed at the carbon atom of the double bond where the nucleophile would add in a Markovnikov addition. Reversal of the regioselectivity has only been observed with particular substrates such as 1,5-dienes [9]. Conversion and selectivity for the oxidation of these olefins were found to be very dependent on the water solubility of the olefin. Indeed, high molecular weight olefins do not react under the standard... 

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