Reductions borane sulfides

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

Various polymer-supported hydrides have been applied successfully to reductions of both carbonyl and olefin groups. Rajasree and Devaky13 describe a cross-linked polystyrene-supported ethylenediamine borane reagent for the selective reduction of aldehydes in the presence of ketones (entry 9). This borane reagent is easily prepared and can be recycled after completion of the reaction. This is a practical alternative to standard borane reagents such as diborane, borane-amine, or borane-sulfide complexes. 

For the oxazaboroHdine-catalyzed reduction of prochiral ketones various borane reductants are employed. Borane-tetrahydrofuran and borane-dimethyl sulfide are the most frequently used reductants. Borane-l,4-thioxane [34], dibo-rane, catecholborane [35, 36, 37, 38], and diethylanihne-borane [39] are also useful borane reductants in this reduction system. 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

Scheme 17 Reduction of nitriles using borane dimethyl sulfide and microwave irradiation...

Aldehydes and ketones have been converted to sulfides by treatment with thiols and pyridine-borane, RCOR -I- R"SH —+ RR CHSR", in a reductive alkylation reaction, analogous to 16-6. 

A novel, unprecedented sulfoxide-directed borane reduction of the a,P-unsaturated sulfoxide to the saturated sulfide was discovered. 

Primary amino methylene substituents were introduced by a sequence of cya-nodehalogenation and subsequent reduction of the resulting nitrile with borane dimethyl sulfide. To incorporate tertiary aminomethylene substituents into the 2-pyri-done framework, a microwave-assisted Mannich reaction using preformed iminium salts proved to be effective. 

Stereoselective reduction of some triazolodiazines (derivatives of ring systems 33 and 37) bearing chiral terpene residues has been elaborated by Groselj el al. <2006TA79>. With catalytic hydrogenation, partial saturation of the six-membered ring was experienced, while reaction with borane-methyl sulfide resulted in formation of triazole-boron complexes. 

First-order kinetics have been found for the reductions of pinacolone by borane-dimethyl sulfide in THF, which proceeds via a monoalkoxyborane complex. In contrast, the kinetics were second order for the reduction with catecholborane and the reactive species was found to be a catecholborane dimer present in small concentrations. 

Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selen-ides under free radical conditions to give the corresponding phosphines or, after treatment with BH3-THF, the corresponding phosphine-borane complex in good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral phosphine sulphides showed that these reductions proceed with retention of configuration. An example is given in Reaction (4.46). 

The chemistry and procedures for modification of the - CO2H groups of PAA hyperbranched grafts on PE powder were analogous to those used for PAA grafts on PE or PP films and wafers. For example, a 90% yield in ester formation was possible using acid-catalyzed Fisher esterification. Likewise, quantitative reduction (ethyl chloroformate activation, borane-dimethyl sulfide reduction) to hyperbranched poly(allyl alcohol)s and amidation all could be carried out using procedures like those used for PAA/Au surfaces. 

Reduction of 5,5-dimethyl-2-pyrrolidone with 3 mol of lithium aluminum hydride by refluxing for 8 hours in tetrahydrofuran gave 2,2-dimethylpyrrol-idine in 67-79% yields [1123]. Reduction of e-caprolactam was accomplished by heating with sodium bis(2-methoxyethoxy)aluminum hydride [544], by successive treatment with triethyloxonium fiuoroborate and sodium borohydride [1121], and by refluxing with borane-d ras. )a.y sulfide complex [1064]. 

An alternative access was achieved by alkylation of the a-diphenylphosphino acetaldehyde SAMP hydrazone 95, yielding the hydrazone products 96 in good yields (60-63%) and good diastereomeric excesses (die = 68-71%) as EjZ mixtures, from which the major diastereomer was separated and purified by preparative HPLC. Ozonolysis and in-situ reduction with the borane-dimethyl sulfide complex of the aldehydes generated gave the air-stable borane-protected 2-diphenylphosphino alcohols 97 in good yields (67-83%). Reaction with DABCO afforded the unprotected 2-phosphino alcohols 98 in very good yields (85-91%) and excellent enantiomeric excesses (ee > 96%) (Scheme 1.1.27). 

Enantioselective reduction of jS-keto nitriles to optically active 1,3-amino alcohols has been carried out in one step using an excess of borane-dimethyl sulfide complex as a reductant and a polymer-supported chiral sulfonamide as a catalyst with moderate to high enantioselectivity (Figure 3.11). The facile and enantioselective method to prepare optically active 1,3-amino alcohols has been used to prepare 3-aryloxy-3-arylpropylamine type antidepressant drugs, for example (l )-fluoxetine. 

This procedure describes the preparation of 3-nitropropanai, 1, employing the rarely encountered 1,4-addition of ambident nitrite ion with its "softer N-atom,2 and further transformations of 1, as reported earlier.3 A similar preparation of 3-nitrobutanal from crotonaldehyde (3-butenal) is known,4 as well as analogous additions to a, 3-enones.2 The reduction of 1 to the alcohol 2, originally carried out with borane-dimethyl sulfide (BMS),3 is now more conveniently and economically done with sodium borohydride. The acetalization of 1 to yield the dimethyl acetal 3 is based on our earlier report.3... 

Some chiral oxazaphospholididine-borane catalysts can be used for enantioselective reduction of prochiral ketones by borane-THF or bor-ane-dimethyl sulfide complex (Scheme 19) (44). 

Borane (as BH3 in tetrahydrofuran or dimethyl sulfide) is an even milder reducing agent than BH4G for the carbonyl group of aldehydes and ketones. This difference in reactivity can be used to advantage when selective reduction is necessary. For example, borohydride reduces a ketone carbonyl more rapidly than a carbon-carbon double bond, whereas borane reduces the carbon-carbon double bond more rapidly than carbonyl ... 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

Selective reduction of ot,a-dihalo ketones." Reduction of a,a-dihalo ketones can he effected without hydrogenolysis of the halo groups with either DIBAH or borane dimethyl sulfide. Reactions with the former reagent are generally faster but work-up can be complicated by gelatinous aluminum salts. In general, the yields are roughly comparable. 

S)-Phenyl-2-oxazolidinone.6 A one-pot route to this chiral auxiliary involves reduction of L-phenylglycine and BF3 etherate in DME with borane-dimethyl sulfide complex at a temperature maintained at 82°. The resulting phenylglycinol is then treated with trichloromethyl chloroformate (or the more expensive triphosgene). 

High-quality albuterol was obtained in good yield from this process. However, several environmental disadvantages were identified. The preparation of the keto aldehyde hydrate (KAH) generated dimethyl sulfide, methyl bromide, and trimethyl-sulfonium bromide (this compound sublimed in the condenser). In addition, reduction of the Schiff base with dimethylsulfide borane, although very attractive in simplifying... 

S) -2-Hydroxy methylindoline (l)1 reacts with borane dimethyl sulfide to form the oxazaborolidine 2, which functions as a catalyst for reduction of ketones by... 

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