THF complex

Booker-Milburn, personal communication K. Booker-Milburn. Synlett. 809 (1992). 

Brandsma and H. Verkruijsse, Preparative Polur Organomelallic Chemistry. Vol. 1, p. 47. Springer-Verlag. Berlin. 1987. 

Savoia, C. Trombini and A. Umani-Ronchi, Synthesis 212 (1986). 

Brandsma and H. D. Verkruijsse, Synthesis of Acetylenes, Allenes and Cumulenes. pp. 16 and 32. Elsevier, Amsterdam, 1981. 

Peralez, J.-C. Negrel and M. Charon, Tetrahedron Lett., 35,5857 (1994). 

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A useful catalyst for asymmetric aldol additions is prepared in situ from mono-0> 2,6-diisopropoxybenzoyl)tartaric acid and BH3 -THF complex in propionitrile solution at 0 C. Aldol reactions of ketone enol silyl ethers with aldehydes were promoted by 20 mol % of this catalyst solution. The relative stereochemistry of the major adducts was assigned as Fischer- /ir o, and predominant /i -face attack of enol ethers at the aldehyde carbonyl carbon atom was found with the (/ ,/ ) nantiomer of the tartaric acid catalyst (K. Furuta, 1991). 

Reaction of 9,10-difluoro-7-oxo-2,3-dihydro-7//-pyrido[l, 2,3- e]-1,4-ben-zothiazine-6-carboxylic acid and its ethyl ester with B(OH)3 in AC2O in the presence of ZnCl2 afforded 6-[(diacetoxyboryl)oxycarbonyl] derivative 323 (R = OAc)], which was reacted with primary and cyclic amines to give 10-amino-9-fluoro-7-carboxylic acid derivatives 324 (97MI41, 98MI30). 6-[(Difluoroboryl)oxycarbonyl derivative 323 (R = F) was obtained from ethyl 9,10-difluoro-7-oxo-2,3-dihydro-7//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylate with BF3-THF complex. Reaction of 323 (R = F) and 1-methylpiperazine in DMF at 50-60 °C and subsequent acidic hydrolysis afforded 7 (97MI1). 

Borane is very reactive because the boron atom has only six electrons in its valence shell. In tetrahydrofuran solution, BH3 accepts an electron pair from a solvent molecule in a Lewis acid-base reaction to complete its octet and form a stable BH3-THF complex. 

Allylmagnesium halides are best prepared from 3-chloropropene and equimolar amounts of magnesium-anthracene THF complex (Table 1, method A)13 -15. Here, usually, the yields arc higher solvent and temperature have only minor influence13 14. A catalytic version is also possible13. 

Propenylmagnesium Chloride, Catalyzed by a Magnesium-Anthracene-THF Complex (Method A) Typical Procedure1,1 ... 

Also, reactive silylene complexes of iron and chromium can be generated at low temperatures and subsequently derivatized by trapping reagents. In THF as solvent, first labile THF adducts are formed, which are converted to the more stable HMPA adducts. The THF complexes dimerize above —40 °C with loss of THF. The silylene complexes can be utilized for reactions if they are generated in the presence of reagents like dimethylcarbonate. The resulting reaction products... 

Cyclisation of l-aryl-6-hydroxyhex-2-ynyl carbonates to the 2-arylidene-5,6-dihydropyran catalysed by Pd(0) is steieospeciBc, giving only the (Z)-isomer <96SL553>, whilst alk-l-yn-5-ols form dihydtopyranylidene carbenes under the influence of the tungsten pentacarbonyl-THF complex. The carbenes are a source of 2-stannyldihydropyrans <96TL4675>. 

Quenching of the same lithiated species with CO2, followed by reduction of the carboxyUc acid functionality obtained with BH3-THF complex, yielded the next higher analogues 78 to these alcohols [94]. Subsequent treatment of the depro-tonated alcohols with TsCl or MsCl afforded (l )-l-boranato[alkyl(methyl)plios-phino] ethanol-2-tosylates or the mesylate phosphine-boranes in over 90% ee and excellent overall yields. 

The same phosphine-borane used for the synthesis of BisP acted as the starting materials of the construction of MiniPHOS, the next smaller analogue to BisP (Scheme 13). The chirally induced lithium salt was treated with alkylphos-phorus dichloride, methylmagnesium bromide, and borane-THF complex to afford enantiomerically pure MiniPHOS-borane 82a. Recrystallization enabled elimination of a small amount of corresponding raeso-diastereomer formed [29]. Yields were generally low, ranging from 13 to 28%. 

We further synthesized unsymmetrical MiniPHOS derivatives 13b (Scheme 13) [30]. Thus, enantioselective deprotonation of l-adamantyl(dimethyl)phos-phine-borane (74, R = 1 -Ad), followed by treatment with ferf-butyldichlorophos-phine or 1-adamantyldichlorophosphine, methylmagnesium bromide and bo-rane-THF complex afforded the optically active diphosphine-boranes 82b as a mixture with the corresponding raeso-diastereomer. Enantiomerically pure unsymmetrical MiniPHOS-boranes 82b were obtained by column chromatography on silica gel or separation by recycling preparative HPLC. 

First, oligo(ethylene oxide) monomethylether was treated with excess BH3-THF complex in THF. After solvent and borane-THF were removed under reduced pressure, the resulting hydroborane with an oligo(ethylene oxide) tail was polymerized with triethyleneglycol in THF at room temperature (r.t.). The polymers obtained were purified by reprecipitation into //-hexane or by washing with diethylether to give colorless or translucent gums in 61—76% yield. 

Amino-2-methoxyphenyl)perhydropyrido[l,2-tf]pyrazine was prepared from a 2-(5-nitro-2-methoxyphenyl)-3-one derivative by catalytic hydrogenation over Pd/C catalyst, followed by the reduction of the 3-oxo group by treatment with BH3-THF complex <1999WO99/042465>. A nitro group was reduced to an amino group in 2-[4-(3-nitrophenyl)piperazin-l-yl]butyl]perhydropyrido[l,2-tf]pyrazine-l,4-dione <2001JME186>, in 8-hydroxy-... 

A solution of BH3THF complex in THF is generally used as the hydroborating agent. Primary hydroboration products 19 and 20 are transformed into the corresponding 1-boraadamantane THF complexes 21 under reflux in THF (1-4 h), or in 4-5 days at room temperature (Scheme 2). 

Hydroboration-isomerization of 33 prepared from triallylborane and phenylprop-l-yne gave the THF complex of 2-phenyl-l-boraadamantane 34 (Scheme 5) <2000IZV497>. 

Oxidation of 1-boraadamantane THF complex 42 with H2O2 in basic media <1979IZV2544> or by trimethylamine iV-oxide dihydrate <2003JA12179, 20010L3063> gave rise to the triol, m, r-l,3,5-tris(hydroxymethyl)cyclohexane 43. The triol 44 was also prepared from the adduct 45 using the first procedure (Scheme 11) <1979IZV2724>. 

Phenyl-l-boraadamantane THF complex 34 <2000IZV497> was transformed into the corresponding pyridine 48 and trimethylamine 16 adducts, the structures being established by X-ray diffraction analysis (Scheme 13) <2002IZV1437>. 

In a molecule of 2-phenyl-l-boraadamantane there are two markedly different types of B-C bonds two of them are boron-alkyl and one is boron-benzyl. On treatment of THF complex 34 with 8-hydroxyquinoline at 20 °C, mpture of the 1-boraadamantane core takes place, resulting in a mixture of boron chelates 52-54 (Scheme 16). When trimethylamine adduct 16 is used as the starting compound, reaction takes place only in boiling toluene. Interestingly, all the products result from the protolysis of B-CH2 bonds only <2006UP1>. 

As mentioned above (Scheme 3), condensation of triallylborane and 3-methoxybut-l-yne led, after treatment with methanol, to 7-(l-methoxymethyl)-3-methoxy-3-borabicyclo[3.3.1]non-6-ene. Hydroboration-isomerization of the latter with a THF solution of diborane gave a THF complex of 2-methyl-1-boraadamantane 15 in 85% yield. Treatment of the latter with (S)-(—)-phenylethylamine gave a mixture of diastereomeric complexes ( ) 57 isolated as white, well-shaped crystals (Scheme 19) <2003MC121, B-2003MI97>. 

Carbonylation-oxidation of the THF complexes (S)-58 and (R)-58 afforded the optically active (3 )-(+)-2-methyl-l-adamantanol (3)-60 and (R)-(—)-2-methyl-l-adamantanol (R)-60, respectively (Scheme 24) <2003MC121, B-2003MI97>. 

A double set of signals in the 13C NMR spectra of THF and pyridine complexes of bridged bis-l-boraadamantanes initially prepared via an allylboron-acetylene condensation-hydroboration sequence shows that these compounds consist of a mixture of racemic and meso-imms <1998IZV728, 2000IZV501, B-2003MI94>. THF complexes show nB NMR shifts at about 12 ppm, whereas the pyridine analogues resonate at about —3 ppm (Table 4). 

The THF complexes of bis(l-boraadamantyl)methane 70, racemic 67a, and a mixture of racemic- and meso-b s( -boraadamantyl)ethane were transformed into the corresponding bis(l-hydroxyadamantyl-2)alkanes 74 and 75 via a standard carbonylation-oxidation procedure (Scheme 30) <2000IZV501, B-2003MI94>. 

Monohomologation of the THF complex of 1-boraadamantane 42 can also be achieved with nucleophilic trimethylsulfoxonium methylide (Scheme 31) and involves a two-step process, consisting of the formation of an ate-complex 83 followed by a [l,2]-migration. Transformation of 42 into 83 is an exothermic reaction. The stmcture of 77 was confirmed by X-ray crystallography <20010L3063, 2003JA12179>. 

The presence of zinc in catalytic proportions promotes formation of the soluble red-violet tetrahydrofuran (THF) complex, Cr(THF)sCl .4... 

Calculations of alkali metal allyl derivatives involving all alkali metals (Li-Cs) indicate a preferred geometry with the metal symmetrically bound in a predominantly electrostatic manner to all three carbon atoms.143 Solution studies of allyllithium in ether indicate the compounds to be highly aggregated in THF complex dynamic behavior is observed. 

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