Pyridine-borane complexes

Innovatory boronated carbons (manufactured in the Institute of Chemistry and Technology of Petroleum and Coal, Wroclaw University of Technology, Poland) were obtained by co-pyrolysis of coal-tar pitch with a pyridine-borane complex. In the first stage of pyrolysis (520°C) the so-called semi-coke is obtained. Further carbonization at 2500°C leads to obtaining boron-doped carbonaceous material (sample labeled 25B2). 

Boron-containing carbons synthesized by co-pyrolysis of coal-tar pitch with pyridine-borane complex (series 25Bn) have already been considered as hosts for lithium insertion [4], Unlike the commercial graphites described above, the boron-doped carbon 25B2 (WUT) as received was not suitable for direct use in the cylindrical cell due to very large and hard particles. This feature makes the coating process very difficult. 

V. T. Perchyonok and Kellie L. Tuck of Monash University found (Tetrahedron Lett. 2008, 49, 4777) that a concentrated solution of Bu NCl and HjPOj in water effected free radical reductions and cyclizations. Stephane G. Ouellet of Merck Frosst demonstrated (Tetrahedron Lett. 2008, 49, 6707) that an oxazoline such as 3 could be converted to the alcohol 4 by acylation followed by reduction. Elizabeth R. Burkhardt of BASF developed (Tetrahedron I tt. 2008, 49, 5152) a protocol for scalable reductive amination using an easily metered liquid pyridine-borane complex. Mohammad Movassaghi of MIT devised (Angew. Chem. Int Ed. 2008, 47, 8909) a strategy for conversion of an allyUc carbonate 8 by way of the ally lie diazene to the terminal alkene 9. 

Amine-borane complexes are not very reactive toward hydroboration, but the pyridine complex of borane can be activated by reaction with iodine.160 The active reagent is thought to be the pyridine complex of iodoborane. 

The following amine boranes are manufd by the Callery Chemical Co a)Dimethylamine-borane, (CH,)aNH BHS, wh solid b)Tri-methylamine-borane, (CHS)SN BH, wh solid e)Pyridine-borane, CBHSN BHb, col liquid These amine-boranes are relatively stable complexes and are of interest because they act as selective reducing agents, polymerization catalysts, anti-oxidants and stabilizing agents. They may also be used for the prepn of diborane and as petroleum additives. Further information may be obtained from Tech Bull C-200(Ref 2)... 

Fu and co-workers have shown that the l-chloro-boracyclohexa-2,4-diene 97 reacts with 4-phenylpyridine at room temperature to provide the />-terphenyl analog 26 in 76% yield as an early example of a borabenzene-pyridine-type complex (Equation 6). The X-ray structure of 26, discussed in Section 7.14.3, shows the three rings not to be coplanar <1997OM1501>. Exposure of the l-chloro-boracyclohexa-2,4-diene 98 to a stabilized carbene results in formation of the complex 29 in 83% yield as an air- and moisture-sensitive colorless powder (Equation 7), crystals of which were grown from toluene the X-ray structure of 29 has been discussed in Section 7.14.3. The use of bulky lithium bases to deprotonate the bis(amido) or bis(alkoxy)boranes 19 allows for the formation of the dianionic 2,2 -diboratabiphenyl derivatives 20 (X = NHPh, OBn), the solid-state structures of which have been discussed (Equation 8) <2006CJC81>. 

Pyridine forms a number of complexes and salts which are useful synthetic reagents. These include pyridinium hydrobromide perbromidc (CjHjNH Brj ), which is a convenient crystalline, easily handled, bromi-nating agent, the pyridine sulfur trioxide complex (C H NrSOj) for sul-fonations, pyridine borane (C HjNrBH,) for hydroborations and the pyridine-chromium(VI) oxide complex (CjHjNiCrOj) for oxidations. 

Reduction of ketones in homogeneous medium in the presence of cyclodex-trins gives disappointing results. However, inclusion of pyridine-borane into ciys-talline P-cyclodextrins generates complexes that reduce prochiral ketones or activated C=C bonds with good enantiomeric excesses [578,579],... 

Greenwood et alP have measured the B shifts of the substituted borane complexes of triethylamine EtaN BH2X (where X = Cl, Br, I and Ph). The B shifts of the complexes of pyridine and substituted pyridine with both borane and phenylborane have been compared the order of the basic strengths was explained in terms of steric strain on the introduction of the phenyl group. 

Nickel and nickel-boron films were prepared by galvanostatic (ik = 2 A/dm2) electrodeposition at 30 °C. Compounds from higher boranes (sodium decahydroklovodecaborate, sodium dodecahydroklovododecaborate) and borane complexes (borane-pyridine, borane-morpholine, borane-dimethylamine, borane-trimethylamine) were used as a source of boron. The thickness of the films was 1-30 pm. The amount of boron in the films was determined by potentiometric... 

The first comes from Jacques Lebreton, and comprises as a key step an enantioselective allylation with (IS)-B-allyldiisopinocamphenylborane, which is readily accessible from allylmagnesium chloride and (IS)-B-chlorodiisopino-camphenylborane. [561] Since the pyridine nitrogen complexes to the borane, at least two equivalents are necessary to obtain good yields and high enantio-selectivity. After mesylation, the azide moiety is introduced with highly selective... 

The insoluble polymeric pyridine-borane system (20) has been reported to reduce aldehydes and ketones in high yields at room temperature in the presence of boron trifluoride-etherate, whereas acid derivatives and a,/3-enones are not reduced. The polymer is used in benzene, and reducing power is better if the polymer beads are swollen in benzene before use. The corresponding polymeric 4-pyridyl-borane (21) is sluggish in reductions but reactivity can be increased using a borane complex of the quaternary polymer (22), which is assumed to... 

Pyridine borane) see Borane pyridine complex Pyrrolidine (Tetramethyleneimine)... 

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. 

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