Reductions alkenes, sodium borohydride

Oxymercuration-reduction of alkenes preparation of alcohols Addition of water to alkenes by oxymercuration-reduction produces alcohols via Markovnikov addition. This addition is similar to the acid-catalysed addition of water. Oxymercuration is regiospecific and auft -stereospecific. In the addition reaction, Hg(OAc) bonds to the less substituted carbon, and the OH to the more substituted carbon of the double bond. For example, propene reacts with mercuric acetate in the presence of an aqueous THF to give a hydroxy-mercurial compound, followed by reduction with sodium borohydride (NaBH4) to yield 2-propanol. 

An alternative route to the erythro.threo diastereoisomeric mixture of alcohols results from the acylation of the alkyldiphenylphosphine oxide with an ester or lactone to yield the /J-ketophosphine oxide, followed by reduction with sodium borohydride. This reduction shows f/ireo-selectivity, so that, following separation of the diastereoisomers, a preparatively useful route to ( )-alkenes is achieved. 

The use of the pseudohalogen nitryl iodide, prepared in situ from iodine and silver nitrite, has been found to add to an alkene in what is strictly an anti-Markownikov fashion. The explanation for this lies in that nitryl iodide adds in a radical manner, initially forming the more stable secondary radical after addition of NO2.115 Treatment of 3-0-acetyl-5,6-dideoxy-1,2-0-isopropylidene-a-D-xy/o-hex-5-enofuranose with nitryl iodide was found to afford an unstable adduct, with the nitro group appended to C-6, and iodine attached to the more substituted C-5.116-118 Similarly, treatment of benzyl 2-0-benzyl-3,4-dideoxy-a-D-g/ycero-pent-3-enopyranoside (70, Scheme 19) with nitryl iodide afforded the unstable adduct 71, which, upon exposure to mild base (NaHC03), afforded the eliminated product, namely benzyl 2-0-benzyl-3,4-dideoxy-4-nitro-a-D-g(ycew-pent-3-enopyranoside (72). The eliminated product was then readily converted into benzyl 2-0-benzyl-3,4-dideoxy-(3-L-r/ireo-pentopyranoside (73) by reduction with sodium borohydride. Addition of deuteride using NaBD4 led to axial deuteration atC-3. 

The introduction of a nitro group into the alkenes under consideration may be achieved by addition of nitryl iodide (IN02). In the case of alkene 22, this addition, followed by reduction with sodium borohydride, led32 to 3-deoxy-1,2 5,6-di-0-isopropylidene-3-C-(nitromethyl)-a-D-allofuranose (52). Light-induced addition of 1,3-dioxolane to alkenes 15a and 22 has also been reported.47 The resulting adducts, 53 and 54, respectively, are of value as they contain a potential aldehydo function. 

Vinyl halides add to allylic amines in the presence of Ni(cod)2 where cod=l, 5-cyclooctodine, followed by reduction with sodium borohydride. Aryl iodides add to alkynes using a platinum complex in conjunction with a palladium catalyst. A palladium catalyst has been used alone for the same purpose, and the intramolecular addition of a arene to an aUcene was accomplished with a palladium or a GaCl3 catalyst, " AUcyl iodides add intramolecularly to aUcenes with a titanium catalyst, or to alkynes using indium metal and additives. The latter cyclization of aryl iodides to alkenes was accomplished with indium and iodine or with Sml2. " ... 

Mercury salts have previously been shown to be capable of cleaving cyclopropyl bonds. Phenyl-substituted cyclopropanes react with mercury(II) acetate to give 3-mercurio-l-methoxy-l-phenylpropane derivatives, which can undergo further reactions such as reduction with sodium borohydride or addition to alkenes. For example, treatment of phenyl-cyclopropane (1) with mercury(II) acetate in methanol, followed by the addition of sodium chloride, produced 3-(chloromercurio)-l-methoxy-l-phenylpropane(2) in good yield.When the primary mercury adduct was reacted with alkenes without isolation, the yields were lower than those in the two-step transformation. ... 

Synthesis of alkyl azides.1 Terminal alkenes and strained cyclic alkenes react with the reagent to give a mercurial intermediate, which on reduction with sodium borohydride gives an azide. Internal olefins do not react. The method is an extension of the hydroxymercuration reaction of Brown (2,265-267). 

The first traceless linker was developed by Kamogawa and coworkers in 1983 [82]. Starting from a polymer-bound sulfonylhydrazine, sulfonylhydrazone resin 88 was formed by reaction with ketones or aldehydes. The cleavage step was conducted either by reduction with sodium borohydride or lithium aluminium hydride to yield alkanes 89 or by treatment with base to give the corresponding alkenes 90 in a Bamford-Stevens reaction (Scheme 16.20). This work was a pioneering approach in the field of traceless tinkers. 

Nickel boride (P — 2) generated from nickel acetate and NaBH4 in ethanol exhibits notable selectivity in reduction depending on the substitution pattern of the alkene " ". Sodium borohydride with Co(II) has also proved to be of general utility for the reduction of various alkenes and alkynes (equation... 

Using rw-chloroalkenes (e.g., 42) in 1,3-dipolar cycloaddition reactions, Pearson et al. described the synthesis of several alkaloids [20-22]. The reaction proceeds by an intramolecular cycloaddition of an azide onto an alkene, producing an intermediate triazohne. Fragmentation of the triazoUne and rearrangement to a monocyclic imine occurs, which is internally N-alkylated by the alkyl chloride, resulting in iminium ion 43. Reduction with sodium borohydride leads to the racemic lycorane (44). 

Methyl-l-hexene is a terminal alkene, and formation of the more stable secondary cation leads to a single major product. However, oxymercu-ration of an unsymmetrical internal alkene leads to a mixture of products. Oxymercuration of 3,3-dimethylcyclopentene, for example, gives a mixture of 74 and 75. Although rearrangement did not occur, two regioisomers are formed because both of the possible carbocation intermediates are secondary. The two mercury-stabilized carbocations are essentially equal in stability, so both are formed and subsequent reaction with water leads to the mixture of alcohols shown after reduction with sodium borohydride. 

Electrophilic Addition to Alkenes, Hydroxy- and alkoxymercurations of alkenes have been performed in micellar SDS. Hydroxymercuration of (1) with mercury(II) acetate, followed by reduction with sodium borohydride, gave a greatly enhanced yield of (2) in micellar SDS (90%) relative to that obtained in THF-H2O (20-25%) (eq 2). Also, the reactions of (1) and the related limonene gave greater cyclic ether diol product ratios in the SDS environment than in aq THF. Both the enhanced 3delds and ratios were attributed to anisotropic solubilization of the alkylmercurial intermediate in a relatively H2O poor mIceUar microenvironment. The hydroxymercuration of an aromatic diene, /Mliallylbenzene, did not display enhanced chemoselectivlty (mono vs. diol formation) in micellar SDS relative to that obtained in THF-H2O. This result suggests that the mIceUar solubilization sites of aromatic substrates and reaction intermediates are more HzO-rich than those of aliphatic systems. 

A method for converting an alkene to an alcohol. The alkene is treated with mercury(Il) acetate followed by reduction with sodium borohydride. 

The aminomercuration-demercuration reaction has provided two examples for primary to secondary amine conversion.In one, Markovnikov addition of the aminomercurial (10) to an alkene, followed by ligand exchange with sodium hydroxide and subsequent reduction with sodium borohydride, yields the secondary amine (11) in a one-pot reaction (Scheme 10). In the other,vicinal diamines (12) are the products from the one-pot reaction of alkenes with tetrafluoroboric acid and mercury(ll) oxide in the presence of excess primary amine (Scheme 11). Both reactions work equally well with secondary amines. 

The reaction sequence includes a variety of different iron complexes and utilizes their specific nucleophilic and electrophilic properties. Nucleophilic addition ofri -allyl-Fp to a tricarbonyliron complexed cationic ri -cycloheptatrienyl system leads to an intermediate (Tj -cycloheptatriene)iron complex bearing an exocyclic cationic (Ti -alkene)iron unit. The latter is attacked by the uncomplexed alkene moiety with concomitant cyciization to leave an alkyl-Fp and an (ri -cycloheptadienylium)iron fragment in the molecule. Reduction with sodium borohydride and subsequent oxidative demetalation in the presence of carbon monoxide provides the hexahydroazulene derivative. 

The nucleophiles that are used for synthetic purposes include water, alcohols, carboxylate ions, hydroperoxides, amines, and nitriles. After the addition step is complete, the mercury is usually reductively removed by sodium borohydride, the net result being the addition of hydrogen and the nucleophile to the alkene. The regio-selectivity is excellent and is in the same sense as is observed for proton-initiated additions.17... 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

Palladium catalysts are more often modified for special selectivities than platinum catalysts. Palladium prepared by reduction of palladium chloride with sodium borohydride Procedure 4, p. 205) is suitable for the reduction of unsaturated aldehydes to saturated aldehydes [i7]. Palladimn on barium sulfate deactivated with sulfur compounds, most frequently the so-called quinoline-5 obtained by boiling quinoline with sulfur [34], is suitable for the Rosenmund reduction [i5] (p. 144). Palladium on calcium carbonate deactivated by lead acetate Lindlar s catalyst) is used for partial hydrogenation of acetylenes to cw-alkenes [36] (p. 44). 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

Vinylamines (enamines) are reduced by alane, mono- and dichloroalane to saturated amines, and hydrogenolyzed to amines and alkenes [710]. Reduction is favored by dichloroalane while hydrogenolysis is favored by alane. Alane, chloroalane and dichloroalane gave the following results with -N-pyrrolidinylcyclohexene V-pyrrolidinylcyclohexane in 13, 15 and 22% yield, and pyrrolidine and cyclohexene in 80, 75 and 75% yields, respectively [710]. Saturated amines were also obtained by treatment of enamines with sodium borohydride [711], with sodium cyanoborohydride [103, 712] (Procedure 22, p. 210) and by heating for 1-2 hours at 50-70° with 87% or 9S% formic acid (yields 37-89%) [320]. 

Azadienes of this sort were studied simultaneously by Mariano et al., who reacted mixtures of (1 ,3 ) and (1E, 3Z)-l-phenyl-2-aza-l,3-pentadiene 275 with several electron-rich alkenes, e.g., enamines and enol ethers (85JOC5678) (Scheme 61). They found the (l ,3 )-stereoisomer to be reactive in this process affording stereoselectively endo 276 or exo 277 piperidine cycloadducts in 5-39% yield, after reductive work-up with sodium borohydride. The stereochemistry of the resulting adducts is in agreement with an endo transition state in the case of dienophiles lacking a cis alkyl substituent at the /8-carbon (n-butyl vinyl ether, benzyl vinyl ether, and 1-morpholino cyclopentene), whereas an exo transition state was involved when dihydropyrane or c/s-propenyl benzyl ether were used. Finally, the authors reported that cyclohexene and dimethyl acetylenedi-carboxylate failed to react with these unactivated 2-azadienes. 

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