Markovnikoff addition

Wilkinson s catalyst has also been utilized for the hydroboration of other alkenes. Sulfone derivatives of allyl alcohol can be hydroborated with HBcat and subsequently oxidized to give the secondary rather than primary alcohol. This reactivity proves to be independent of substituents on the sulfur atom.36 Similarly, thioalkenes undergo anti-Markovnikoff addition to afford a-thioboronate esters.37 The benefits of metal-catalyzed reactions come to the fore in the hydroboration of bromoalkenes (higher yields, shorter reaction times), although the benefits were less clear for the corresponding chloroalkenes (Table 3).38,39 Dienes can be hydroborated using both rhodium and palladium catalysts [Pd(PPh3)4] reacts readily with 1,3-dienes, but cyclic dienes are more active towards [Rh4(CO)i2].40... 

An extensive array of chiral phosphine ligands has been tested for the asymmetric rhodium-catalyzed hydroboration of aryl-substituted alkenes. It is well known that cationic Rh complexes bearing chelating phosphine ligands (e.g., dppf) result in Markovnikoff addition of HBcat to vinylarenes to afford branched boryl compounds. These can then be oxidized through to the corresponding chiral alcohol (11) (Equation (5)) ... 

Hydroamination involves the addition of primary or secondary amines to alkenes to afford terminal or branched higher value substituted amines via anti-Markovnikoff or Markovnikoff addition.144 Although the addition of RNH2 to C=C is thermodynamically favorable (Equation (14)), there is a strong entropic factor disfavoring N-H addition which has to be overcome through use of a metal catalyst. 

Thiol Alkene+H2S (peroxide or UV) (Anti-Markovnikoff addition)... 

Reduction of alkenes to alcohols.3 The combination of TiCI4 and NaBH4 in DMF produces a low-valent titanium-borane complex that converts alkcncs to alcohols in which the hydroxy group is introduced by an anti-Markovnikoff addition. 

CO-NMe insertion to give (86) and (87). The same workers have also shown that in methanol solution and in the presence of 1,1-diphenylethylene, (79) acts as a typical electron transfer photosensitizer for the anti-Markovnikoff addition and 2,2-diphenylethyl methyl ether is formed in 70% yield with 93% of (79) being recovered. 

The halohydroxylation method has been developed for exploiting the reactivity of the double bond present in dialkyl vinyl- and propenylphosphonates. Preparation of the halohydrins of diethyl vinylphosphonate failed using NBS or NBA. Treatment of diethyl vinylphosphonate on large scale with NaOCl or NaOBr in aqueous medium at pH < 3 gives the halohydrins with the hydroxyl group in the P-position (anti-Markovnikoff addition) with 95% or 65-85% purity, respectively (Scheme 4.9). As a consequence of the acid conditions, the preparation of halohydrins is generally accompanied by the formation of undesired diethyl 1,2-dihalogenophosphonates. ... 

Photo-oxidation of limonene in pyridine in the presence of U02(0Ac)2,2H20 proceeds by anti-Markovnikoff addition of hydroxy-radical followed by reaction with molecular oxygen to yield (148). The identical photoreactions of methanol with pulegone (21) in the presence of TiCU and UO2CI2 (Vol. 7, p. 8) have now been reported in full. Sensitized photoaddition of methanol to carvone (18), ... 

In 1956 Herbert C. Brown (b. 1912) discovered that in ethereal solution diborane (B2H5) dissociates into borane (BH3), which can add to an alkene. The organoborane formed can be converted to an alcohol by treatment with hydrogen peroxide, and the overall result of this hydroboration reaction is the anti-Markovnikoff addition to the double bond. Brown was also responsible for the introduction into organic chemistry of the reducing agents sodium borohydride (sodium tetrahydridoborate(lll)) and lithium aluminium hydride (lithium tetrahydridoaluminate(lll)). 

The known anti-Markovnikoff addition of thiyl radicals to double bonds has been utilized in a synthesis of the 3-methylenecepham methyl ester (115) by irradiation of a dilute solution of benzothiazolyldithioazetidinone (114) in acetonitrile (60% yield) irradiation of more concentrated solutions of (114)... 

Hydrogen sulfide adds to olefins and unsaturated compounds to give thiols in good to excellent yields. The reaction is usually very rapid and is catalyzed either by free radical initiators (peroxides or ultraviolet light) or ionic types of catalysts such as transition metals, sulfuric acid, or even free sulfur. The free radical initiated reaction addition gives anti-MarkovnikolT addition products [Eq. (10)] whereas the ionic catalyzed reaction gives Markovnikoff addition products [Eq. (11)]. Both types of reactions work well in the laboratory and are also practiced commercially. 

Malonic ester synthesis, 60, 74 Mannich reaction, 157 Markovnikoff addition, 178 anti-, 178, 180 Markovnikoff s rule, 29 McFadyen-Stevens reaction, 50 Michael condensation, 157 Michael reaction, 94... 

Mannig and Noth reported the first example of rhodium-catalyzed hydroboration to C=C bonds in 1985.4 Catecholborane reacts at room temperature with 5-hexene-2-one at the carbonyl double bond when the reaction was run in the presence of 5mol.% Wilkinson s catalyst [Rh(PPh3)3Cl], addition of the B—H bond across the C=C double bond was observed affording the anti-Markovnikoff ketone as the major product (Scheme 2). Other rhodium complexes showed good catalytic properties ([Rh(COD)Cl2]2, [ Rh(PPh3)2(C O )C 1], where... 

Wilkinson s catalyst brings about the hydrosilylation of a range of terminal alkenes (1-octene, trimethylvinylsilane) by 2-dimethylsilylpyridine with good regioselectivity for the anti-Markovnikoff product. Both 3-dimethylsilylpyridine and dimethylphenylsilane are less reactive sources of Si-H. In contrast, these two substrates are far more reactive than 2-dimethylsilylpyridine for the hydrosilylation of alkynes by [Pt(CH2 = CHSiMe2)20]/PR3 (R = Ph, Bu ). This difference was explained to be due to the operation of the two different pathways for Si-H addition—the standard Chalk-Harrod pathway with platinum and the modified Chalk-Harrod pathway with rhodium.108... 

The first example of anti-Markovnikoff hydroamination of aromatic alkenes has been demonstrated with cationic rhodium complexes.170 A combination of [Rh(COD)2]+/2PPh3 in THF under reflux yields the N-H addition product as the minor species alongside that resulting from oxidative amination (Scheme 37). Hydrogenation products are also detected. 

If the more activated alkene 2-vinylpyridine is used in place of styrene with the same catalysts and the same range of substrates, anti-Markovnikoff hydroamination is also found. Thus, N-[2-(2 -pyridyl)ethyl]piperidine was isolated in 53% yield from reaction of 2-vinylpyridine with piperidine in the presence of [Rh(COD)2]+/2PPh3 under reflux. N H addition was observed with other amines, the remaining product in all cases being primarily that from oxidative amination (Table 12). When the catalytic reaction was run in the absence of phosphine, the yield of hydroamination product increased dramatically.171... 

Addition of the P—H bond of hydrogen phosphonates (R0)2P(0)H across alkynes (hydrophosphorylation) may be catalyzed using both Pd° and Pd11 complexes.196 Reaction of oct-l-yne with either (MeO)2P(0)H or (EtO)2P(0)H affords the Markovnikoff adduct (Equation (18)) as the... 

Mark-Houwink equation phys chem The relationship between intrinsic viscosity and molecular weight for homogeneous linear polymers. mark hau.wigk l.kwa-zhan Markovnikoff s rule org chem in an addition reaction, the additive molecule RH adds as H and R, with the R going to the carbon atom with the lesser number of hydrogen atoms bonded to it. mar kov-ns.kofs, riil ... 

Addition of nucleophiles to 1,1-diarylethylenes has also been reported to give the anti-Markovnikoff product158, interestingly, solvent polarity may have a strong effect on the stereochemistry of addition (Scheme 64), though no mechanism has been suggested which explains this result1586. 

The regioselective addition of HX to alkenes produces the more substituted alkyl halide, which is known as the Markovnikov (Markovnikoff) product. Markovnikov s rule states that on addition of HX to an alkene, H attaches to the carbon with fewest alkyl groups and X attaches to the carbon with most alkyl groups . This can be explained by the formation of the most stable intermediate carbocation. 

The reaction of 231 with styrene was catalyzed by boron trifluoride to give the Markovnikoff adduct 232 (equation 113), while the addition of 231 to cyclohexene gave solely the trans adduct 233. The uncatalyzed reaction with styrene afforded the anti-Markovnikoff adduct 234 (equation 114). The reaction of selenolsulfonates with acetylenes proceeds in refluxing benzene or chloroform without boron trifluoride ethe-rate103 104, and produces only a single adduct 237 in a stereo- and regioselective fashion (equation 115). The addition of selenolsulfonates to acetylenes is shown in Table 10. When... 

In common with simple thiols and (9, (9-dialkyl phosphorodithioates, phosphinodithioic acids add to alkenes according to the Markovnikoff rule (propenenitrile is a possible exception to this behaviour) and even in the absence of a catalyst (equation 44). In the presence of sodium methoxide, anti-Markovnikoff behaviour is often observed as the result of Michael addition of the acid anion (equation 45). Addition of the acids to otherwise saturated nitriles leads, following acidolysis of intermediate species, to thiocarboxamides and the phosphinothioyl halide (Scheme. 50). 

The concerted nature of the reaction is indicated by the fact that a Markovnikoff-type directing effect is essentially absent. Secondary and tertiary products are formed in nearly equal amounts from unsymmetri-cally substituted olefins (9, 13, 14, 15, 17, 27, 34). In addition, substituents on the phenyl group of trimethylstyrene exert no effect on the product distributions (12). Furthermore, values for 2-methyl-2-pentene show only a very small solvent effect (12). All these facts suggest that little polarity is developed at the transition state and are consistent with a concerted reaction. 

The electrophilic addition reactions of A -unsaturated steroids and other rigid cyclohexenes are controlled mainly by the conformational preference for diaxia) addition HOBr, for example, gives mainly a 5a-bromo-6)5-alcohol. A study of similar reactions with B-nor-A -unsaturated steroids suggests that the reaction of a cyclopentene is under electronic rather than conformational control.A variety of reagents (HOBr, BrF, Brj, BrOMe, and BrOAc) gave mainly 6a-bromo-5)S-substituted derivatives (155), indicating that the initial product, a 5a.6a-bromonium ion (154). reacts further according to Markovnikoff, with attack of the anion at the tertiary 5 -position. 

Arts. Markovnikoff s rule is used The H fragment from the reagent adds to that carbon of the double bond which already has more hydrogens. The rule is often stated as The rich (in hydrogens) get richer. For addition of HCl to 1-butene, C-1 receives H from HCl since it has more hydrogens than C-2. 

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