Tetrahydrofuran complexes

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" ... 

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-... 

Catalytic cyclopropanation of alkenes has been reported by the use of diazoalkanes and electron-rich olefins in the presence of catalytic amounts of pentacarbonyl(rj2-ris-cyclooctene)chromium [23a,b] (Scheme 6) and by treatment of conjugated ene-yne ketone derivatives with different alkyl- and donor-substituted alkenes in the presence of a catalytic amount of pentacarbon-ylchromium tetrahydrofuran complex [23c]. These [2S+1C] cycloaddition reactions catalysed by a Cr(0) complex proceed at room temperature and involve the formation of a non-heteroatom-stabilised carbene complex as intermediate. 

These changes are more consistent with an /-effect, rather than an R-effect, on the B—C bond. That such diborylacetylenes have a diminished electron density at boron relative to alkyl- and vinylboranes is evident from their enhanced Lewis acidity bis(diethylboryl)acetylene (40) forms a bis(tetrahydrofuran) complex, as is evident from the1 B NMR spectrum37 (Eq. 11). Alkyl- and vinylboranes exhibit no such shifts in their11B signals in THF solution. 

The A-trimethylsilylimines 68 (R = t-Bu, Ph, 2-MeCgH4 or 2-BrC6H4), which are prepared by the reaction of non-enolizable aldehydes with lithium bis(trimethylsilyl)amide, followed by trimethylsilyl chloride, undergo pinacolic coupling induced by NbCLt 2THF to yield the vicinal diamines 69 as mixtures of dl- and meso-isomers, in which the former predominate. Another method for the preparation of 1,2-diamines is by the combined action of the niobium tetrachloride/tetrahydrofuran complex and tributyltin hydride on cyanides RCN (R = /-Hu. Ph, cyclopentyl or pcnt-4-en-l-yl) (equation 32)82. 

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

Measured in toluene-d. Complexes with L = 17a, 17c measured in 2-methyl tetrahydrofuran, complexes with L = 17b, 17d measured in cyclohexane. 

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. 

Vandenberg (77) has found that vinylethers are polymerized by combinations of vanadium tetrachloride and triethylaluminum. Vandenberg believed that the intermediate vanadium trichloride, produced by reduction of the vanadium tetrachloride, reacted with the triisobutyl-aluminum-tetrahydrofuran complex to produce the modified Friedel-Crafts catalysts that converted the vinylether to isotactic polymer. 

Number of surface OH groups as determined by pulse titration with dimethylzinc tetrahydrofuranate complex in helium at 363 K according to ref. 11 catalyst epretreatment 773 K, 2 h. 

A 0.5 M solution of 9-BBN in tetrahydrofuran was purchased from Aldrich Chemical Company, Inc., and was used without additional purification. The preparation2 of the reagent by hydroboration of 1,5-cyclooctadiene with borane/tetrahydrofuran complex is reported. 

Compound with 9S-cinchonan-9-ol (3974950-3), 67, 1 Borane-dimethylsulfide (13292-87-0), 68, 77 Borane, tetrahydrofuran complex, 69, 214... 

This compound was obtained as tetrahydrofuran complexes of two and three molecules of solvation. They were mildly pyrophoric. 

Schmidt, G, Enkelmann, V., Westphal, U., Droscher, M., and Wegner, G. (1985) Preparation of urea-poly(tetrahydrofuran) complexes and their application for fractionation of oligomers, Colloid Polym. Sci. 263, 120-127. 

On the basis of tetrahydrofuran complexes of pentacarbonyls of Group VI metals and triphenyl derivatives of Group V elements, the binuclear complexes with M — E bond were isolated (3.208) [453] ... 

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