Boran-tetrahydrofuran

A more convenient hydroboratmg agent is the borane-tetrahydrofuran complex (H3B THF) It IS very reactive adding to alkenes within minutes at 0°C and is used m tetrahydrofuran as the solvent... 

Examine the electrostatic potential map of H3B THE (borane-tetrahydrofuran complex) on Learning By Modeling How does the electrostatic potential of the hydrogens bonded to boron dif fer from the potential of the hydrogens of the tetrahydrofuran ring" ... 

Diborane [19287-45-7] the first hydroborating agent studied, reacts sluggishly with olefins in the gas phase (14,15). In the presence of weak Lewis bases, eg, ethers and sulfides, it undergoes rapid reaction at room temperature or even below 0°C (16—18). The catalytic effect of these compounds on the hydroboration reaction is attributed to the formation of monomeric borane complexes from the borane dimer, eg, borane-tetrahydrofuran [14044-65-6] (1) or borane—dimethyl sulfide [13292-87-0] (2) (19—21). Stronger complexes formed by amines react with olefins at elevated temperatures (22—24). 

Scheme 4 outlines the synthesis of key intermediate 7 in its correct absolute stereochemical form from readily available (S)-(-)-malic acid (15). Simultaneous protection of the contiguous carboxyl and secondary hydroxyl groups in the form of an acetonide proceeds smoothly with 2,2 -dimethoxypropane and para-toluene-sulfonic acid and provides intermediate 26 as a crystalline solid in 75-85 % yield. Chemoselective reduction of the terminal carboxyl group in 26 with borane-tetrahydrofuran complex (B H3 THF) affords a primary hydroxyl group that attacks the proximal carbonyl group, upon acidification, to give a hydroxybutyrolactone. Treat-... 

Diborane, Bis(2-methoxyethyl) ether See Borane-tetrahydrofuran (reference 3)... 

Nonmetallic systems (Chapter 11) are efficient for catalytic reduction and are complementary to the metallic catalytic methods. For example lithium aluminium hydride, sodium borohydride and borane-tetrahydrofuran have been modified with enantiomerically pure ligands161. Among those catalysts, the chirally modified boron complexes have received increased interest. Several ligands, such as amino alcohols[7], phosphino alcohols18 91 and hydroxysulfoximines[10], com-plexed with the borane, have been found to be selective reducing agents. 

The temperature has a significant effect on the selectivity of the reaction, with the optimal temperature being dependent on the borane source. The optimal range of temperature was 25 °C when borane-dimethylsulfide was used and 0-5 °C when borane-tetrahydrofuran was used as the reducing agent (Table 11.5). 

Benzyl bromide, Molecular sieve, 2735 Benzyl chloride, Catalytic impurities, 2738 1,2-Bis(chloromethyl)benzene, 2946 Bis(2-cyanoethyl)amine, 2397 Bis(trimethylsilyl) peroxomonosulfate, 2602 Borane -tetrahydrofuran, 0138 Butylmagnesium chloride, 1641 Calcium acetylide, Methanol, 0585 Calcium chloride, 3923 Cerium, Water, 3961... 

Acrylic acid, Initiator, Water, 1148 Aluminium chloride, Water, 0062 Barium peroxide, Propane, 0216 1,3-Benzodithiolium perchlorate, 2677 1,1 -Bis(fluorooxy)tetrafluoroethane, 0641 Borane-tetrahydrofuran, 0138 Boron tribromide, Water, 0122 Bromine, Aluminium, Dichloromethane, 0261 Bromine, Tungsten, Tungsten trioxide, 0261 f 1,3-Butadiene, 1480 Calcium oxide, Water, 3937 Chlorine trifluoride, Refractory materials, 3981 Chromium trioxide, Acetic acid, 4242 Copper(II) oxide, Boron, 4281 Diazoacetonitrile, 0675 Dihydroxymaleic acid, 1447 Ethyl azide, 0872... 

Mono(2,6-dimethoxybenzoyl)tartaric acid Butanedioic acid, 2-[(2,6-dimethoxybenzoyl)oxy-3-hydroxy-, [R-(R, R )]- (12) (116212-44-3) 2,6-Dimethoxybenzoic acid Benzoic acid, 2,6-dimethoxy- (8,9) (1466-76-8) Trifluoroadetic anhydride Acetic acid, tritluoro-, anhydride (8,9) (407-25-0) Borane-Tetrahydrofuran Furan, tetrahydro-, compd. with borane (1 1) (8,9) (14044-65-6)... 

Borane-tetrahydrofuran complex Furan, tetrahydro, compd. with borane (1 1) (8,9) (14044-65-6)... 

Hydroboration-oxidation is a useful method when the desired product is the anti-Mcirkovnikov alcohol. The borane-containing reactant is normally dibo-rane (B2Hg) or the borane tetrahydrofuran complex (BHj THF). No matter what hydroboration agent is used, it s usually simplified to BH3 in the mechanism. BH3 is a useful reactant because it s a good Lewis acid. 

Introduction of the C2 sulfonamide is accomplished via sulfonylation with chlorosulfonic acid, conversion to the sulfonyl chloride using thionyl chloride, and amidation using concentrated ammonium hydroxide in tetrahydrofuran. Reduction of the 4-acetamido compound using borane-tetrahydrofuran complex provides the 4-ethylamino derivative. The 45,65-frans diastereomer is selectively crystallized as its maleate salt from acetone in the presence of the unwanted 4R,6S-cis diastereomer. Neutralization of the maleate salt and extraction of the free base in ethyl acetate, followed by formation of the hydrochloride salt, yields crude dorzolamide hydrochloride. 

Bei einem anderen Verfahren zur Herstellung von optisch-aktiven Aminoalkanen aus Oxim-Derivaten reduziertman O-Alkyl-oxime, deren Alkyl-Gruppe (evtl. auch funktionell substituiert) mit einem asymmetrischen C-Atom an die Hydroximino-Gruppe gebunden ist1. Auf diese Weise erhalt man z.B. durch Reduktion von chiralem Acetophenon-[0-(l-carboxy-ethyl)-oxim] mit Boran-Tetrahydrofuran (S)-1-Amino-1-phenyl-ethan in 72% chemischer Ausbeute und einem ee-Wert von 40%. 

Die Reaktion von O-Methyl-benzaldoxim mit Organolithium-Verbindungen, gefolgt von der Reduktion des intermediar gebildeten N-Lithio-ketimins mit Boran-Tetrahydrofuran ergibt sek.-Alkyl-amine2 ... 

All of the following manipulations are performed under argon using standard Schlenk techniques. Solvents are degassed and distilled under nitrogen immediately before use unless otherwise noted. (Cp RuCl2)2 is available from Strem Chemicals, Inc., and is used as received. Lithium borohydride, LiBEU (2.0 M in tetrahydrofuran), and borane tetrahydrofuran, BH3 THF (1.0 M in tetrahydro-furan), are available from Aldrich Chemical Co. and are used as received. Note that these solutions decrease in molarity depending on time and use, and, if solutions are not titrated before use, appropriate increases in the volumes of solution used may be required. 

Borane-tetrahydrofuran is commercially available from Aldrich Chemical Company, Inc. When a fresh bottle is used, titration is not necessary. 

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