Markovnikov-type addition

PSL, AMANO) has been found to catalyze the Markovnikov-type addition of thiols to vinyl esters (Scheme 5.23) [114] and acylases aminoacylase [115], penicillin G acylase [116], and acylase from AspergiUus oryzae [117], the same kind of addition of various nitrogen nucleophiles. Unfortunately, most additions described above are nonstereoselective. 

Both products result from a Markovnikov-type addition. The same regioselectivity was obtained using 1-hexene as olefin [161]. 

Hydrogen bromide adds to carbon-carbon double bonds, usually the Markovnikov-type addition, forming bromo derivatives ... 

In contrast, reactions of esters of unsaturated acids with the sulfur tetrafluoride/hydrogen fluoride/chlorine reagent result in formal addition of C1F across the C = C bond to formchloro-fluoroalkanoic acid esters. The Markovnikov-type addition occurs in reactions with methacrylic and but-2-enoic esters to give 3-chloro-2-fluoro esters, e.g. 17, while from acrylic esters anti-Markovnikov products, 2-chloro-3-fluoro esters, e.g. 16, are formed.242... 

Because the reaction is catalytic in ferf-butyl cation and the deprotonation/ reprotonation steps are very fast, extensive regioselective deuteriation of the isoalkane is observed at room temperature as shown by GC-MS analysis. The absence of mass 68 (d10-isobutane) and the presence of mass 64 due to S02 formation in the oxidative process are typical features in accord with the oxidative activation of the alkane and the Markovnikov-type addition of deuterons on the intermediate isobutylene (14). However, the exchange process does not take place in the presence of carbon monoxide, which traps the ferf-butyl cation and prevents deprotonation (Scheme 5.7). 

Intermolecular Markovnikov-type addition of phenols (ArOH), carboxylic acids (RCO2H), and protected amines (TsNH2) to alkenes, such as 4-MeOC6H4CH2CH= CH2, can be catalysed by triflic acid in low concentrations (1-5%). Functional groups, such as the methoxyl on aromatics, can be tolerated if the concentration of triflic acid and the reaction temperature are controlled appropriately. This reaction provides one of the simplest alkene addition methods and can serve as an alternative to metal-catalysed reactions.33... 

An efficient protocol for Markovnikov-type addition of N-hclcrocycles (imidazole, pyrazole, pyrrole, etc.) to the electron-rich double bond of vinyl esters using ionic liquid as a catalyst has been reported.40... 

Both chlorine and bromine triflates react with HFP to give only one, Markovnikov type, additional product, which is yet further evidence of the electrophilic mechanism of the process, since radical addition of CF3OF to F-propene produces a mixture of two regio isomers [35] ... 

Vinyl pyrazines (44) have been shown to react with benzene in the presence of CF3S03H to afford anti-Markovnikov-type addition products (45). This unusual outcome suggests that acid-catalysed addition reactions can give anti-Markovnikov-type products when a multiply charged (i.e. superelectrophilic) group is adjacent to the... 

The first examples of hydration of alkynes catalyzed by gold salts were reported in 1976 by Thomas." Later, Utimoto found that the reaction could be carried out with lower amounts of catalyst." Tanaka and coworkers reported a general hydration of alkynes using cationic Au(I) complexes generated in situ by protonolysis of [AuMe(PPh3)] as depicted in equations (2) and (3). Markovnikov-type addition is observed in all cases. Other complexes of Au(I) and Au(III) have proved to be effective in this reaction. The somewhat related gold-catalyzed addition of HCl to alkynes is an industrial process for the generation of vinyl chloride. " ... 

As in the foregoing systems, a regiochemical ambiguity arises unless the alkene is either symmetrical or highly biased toward Markovnikov-type addition. Both acid chlorides and bromides can be employed. Aluminum trichloride is the preferred reagent." Frequently the divinyl ketone or P -chloro enone intermediates are isolable as by-products which can be sub quently cyclized. Representative structures are similar to those collected in Scheme 35. 

The exocyclie double bond of 6-metboxy-2-vinyl naphthalene underwent a totally regiose-lective, Markovnikov-type addition of HCN in the presence of less than 1 mol% of (D)-glu-cose-derived phosphinite ligand 88 and of Ni(COD)2 in toluene to afford nitrile 89 in more than 85% yield and up to 85% e.e. The e.e. was improved to >99% by two crystallizations. Acid hydrolysis of 89 gave (S)-22 in high yield and unaltered e.e. 

The hydroformylation of propylene provides two types of products, n- and isobutyraldehydes depending on the insertion modes of propylene into the M-H bond. As shown in Scheme 1.18a and b, where R = H, the anti-Markovnikov type addition of M-H to the double bond in (a) gives the linear propyl, whereas the Markovnikov type addition gives the isopropyl group bound with the metal. Further insertion of CO yields the linear and branched acyl groups. 

The new oxapalladacycle (43), readily obtained via direct ortho-palladation of Ph2P(0)0H with (AcO)2Pd, has been reported to catalyse Markovnikov-type additions of E-H bonds (E-H = R 2PH, PhSH, and R CH=CH) to terminal alkynes RC CH, producing methylene compounds RC(E)=CH2. ° ... 

Morphological control of heterogeneous Pd and Ni particles has led to development of superior catalysts for regioselective Markovnikov-type addition of RZH to terminal alkynes and stereoselective addition to internal alkynes under mild conditions. 

Heteroatom compounds bearing a P—H linkage such as (R0)2P(0)H and R2P(0)H also add to alkynes in the presence of palladium catalyst. When the Markovnikov-type addition to alkynes takes place selectively, the iyn-addition process is operative. 

Keywords Alkynes, iodine/hydrophosphine binary system, CDCI3, room temperature, regioselective hydroiodination, Markovnikov-type addition, vinyl iodides... 

Markovnikov-type addition of benzenethiols to alkynes has been investigated in detail by using nickel catalysts such as nickel dichloride (NiCl2) [28]. The NiCl2-catalyzed hydrothiolation of alkynes with PhSH has been attained by using y-terpinene and triethylamine as additives (Scheme 8). 

Another example of nickel-catalyzed hydrothiolation of alkynes is reported. Ni (PPh2Me)4 in the presence of Ph2P(0)0H works as a useful catalyst for the Markovnikov-type addition of 1-octyne [34]... 

C-H activation reactions [35]. Rhodium pyrazolylborates, as highly electron-rich metal complexes, are found to be useful catalysts for the Markovnikov-type addition of thiols to alkynes. In particular, Tp Rh(PPh3)2 (Tp = hydrotris (3,5-dimethylpyrazolyl)borate) exhibits an excellent catalytic activity toward the regioselective hydrothiolation of a range of alkynes with both arene- and alkanethiols (Scheme 11) [36 0]. A variety of functional groups are well tolerated, and both sterically encumbered alkynes and thiols are successful in hydrothiolation. Electron-rich alkynes react more rapidly than electron-deficient alkynes. 

Hydrothiolation of terminal alkynes is investigated by using Tp Rh(SPh)2 as the catalyst [41]. This hydrothiolation also affords Markovnikov-type addition products as the major product. Mechanistic aspects are shown in Scheme 12. 

In the transition-metal-catalyzed Markovnikov-type addition of thiols to terminal alkynes, the double-bond-isomerization reactions of the formed Markovnikov addition products 1 are often observed, when the propargylic protons are present in alkynes. As already mentioned, the addition of amines to the reaction systems suppresses the formation of the double-bond-isomerization product 2. On the other hand, the use of PdCl2(PhCN)2 as a catalyst causes Markovnikov addition of PhSH to terminal alkynes and the following double-bond-isomerization reaction, which afford 2-phenylsulfanyl-2-alkene 2 as the major product (Scheme 15) [7, 48]. 

A variety of alkynes undergo regio- and stereoselective hydrothiolation with arenethiols in the presence of RhCl(PPh3)3. Ethanol and dichlorometane is suitable solvents for this hydrothiolation. This hydrothiolation proceeds well, even when galvinoxyl as a radical inhibitor is added to the reaction system. Recently, Wilkinson s catalyst is reported to be an excellent catalyst for alkyne hydrothiolation with alkanethiols to provide -isomers of anri-Markovnikov-type addition products 3 selectively [54]. 

A simple heterogeneous nickel-based catalytic methodology is developed for regioselective hydroselenation of terminal alkynes (selective Markovnikov-type addition) and stereoselective hydroselenation of internal alkynes (selective sy -addition) [93]. The catalytic transformation is performed under mild conditions, thus avoiding byproduct formation. 

Indium(l) iodide is found to promote the regio- and stereoselective hydrothiolation of propargyl alcohols with (PhSe)2 (Markovnikov-type addition and anfi-addition)... 

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