Anti-Markovnikoff product

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... 

Hydrophosphorylation has recently been extended to rhodium catalysts as a route to anti-Markovnikoff products.198 Thus, 3mol.% Rh(PPh3)3Cl affords the ( )-alkenylphosphonates (R = H, Ph, -Cr,I I ]3, CH2CH2CN, SiMe3, or cyclohexenyl) in high yields (>80%) at room temperature when 4,4,5,5-tetramethyl-l,3,2-dioxaphospholane-2-oxide (74) is used as the PH source (Equation (19)).199 The rate of reaction is highly solvent dependent... 

Propanol has been manufactured by hydroformylation of ethylene (qv) (see Oxo process) followed by hydrogenation of propionaldehyde or propanal and as a by-product of vapor-phase oxidation of propane (see Hydrocarbon oxidation). Celanese operated the only commercial vapor-phase oxidation faciUty at Bishop, Texas. Since this faciUty was shut down ia 1973 (5,6), hydroformylation or 0x0 technology has been the principal process for commercial manufacture of 1-propanol ia the United States and Europe. Sasol ia South Africa makes 1-propanol by Fischer-Tropsch chemistry (7). Some attempts have been made to hydrate propylene ia an anti-Markovnikoff fashion to produce 1-propanol (8—10). However, these attempts have not been commercially successful. 

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... 

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... 

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. 

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