Triethylamine, borane complexes

Borane—triethylamine complex (4) is used when slow Hberation of borane at elevated temperatures is advantageous, eg, in the cycHc hydroboration of trienes to avoid the formation of polymers (59). 

Hydroboration of acyclic trienes with 1 1 H3B THF at 0°C leads to insoluble products. Monomeric bicyclic boranes are produced in low yields. These organoboranes are obtained, however, either by thermal treatment of the insoluble products or directly by hydroboration of trienes with borane-triethylamine complex . ... 

Borane-triethylamine complex proceeds similarly as a hydroborating agent. Low concentration of borane in the mixture provided by slow thermal dissociation of the complex is advantageous in these hydroborations facilitating the formation of cyclic products . 

The hydride donor ability of Hantzsch ester 4a has been experimentally determined to be slightly higher than that of N-benzylnicotinamide, both being comparable to the borane-triethylamine complex [17]. Together with trichlorosilane [18], Hantzsch esters 4 are the reagents of choice to effect asynunetric reductions using chiral organocatalysts. 

A solution of 4 (110 mg, 0.26 mmol) in a mixture of dichloromethane (25 mL) and methanol (8 mL), cooled to —78°C, was ozonized until the solution turned blue (about 4 min). Excess ozone was removed by a stream of nitrogen, the solution was allowed to attain room temperature and was concentrated to dryness. The crude product was dissolved in THF (10 mL) and a borane-THF complex (1.04 mL of a -M solution) was added at room temperature under nitrogen. After 24 h the reaction mixture was treated with diluted hydrochloric acid (5 mL) and the solution was extracted with ethyl acetate (4x15 mL). The combined extracts were dried (MgS04) and concentrated to dryness. The residue was dissolved in dichloromethane (20 mL) and acetylated with acetic anhydride (62 p,L, 0.66 mmol), triethylamine (200 p,L, 1.50 mmol), and a crystal of DMAP, under nitrogen atmosphere. After 12 h the reaction mixture was concentrated under diminished pressure, and the crude product was purified on a silica gel column with hexane-ethyl acetate (3 1) to give 5 (73 mg, 65%) mp 103°-105°C (after crystallization from hexane), [a]D — 26.6° (c 0.7, CHC13). 

The enantioselective deprotonation of the borane complex 248 of A-methylisoindoline was investigated by Simpkins and coworkers (eqnation 59) . Deprotonation with i-BuLi/(—)-sparteine (11) in diethyl ether at —78°C for 1 h, followed by quenching with chlorotrimethylsilane, yielded the silanes 251, ent-252, 252, ent-25 in a ratio of 86.3 0.4 6.3 7.0 after destroying the chiral centre at nitrogen by treatment of the whole mixture with triethylamine, an e.r. 253/ewf-253 of 86.7 13.3 is expected. 

Similar claims are also made for diphenylamine-borane, which is a solid and relatively stable re-agent. Aliphatic amine-borane complexes, however, require elevated temperatures in order to effect hydroboration.Although this is in general a serious drawback, on occasions it may be advantageous by allowing slow liberation of borane, which leads to cyclization products rather than polymers. An example of the use of triethylamine-borane in this way is shown in equation (11). ° Alternatively, methyl iodide or a Lewis acid may be added to complex the amine and thus liberate the reactive, free borane... 

Complexation of the latter at phosphorus with borane, followed by methanolysis of the siloxyether function, gives the related o-hydroxyaryl diazaphospholidines. The cage-like triaminophosphine (109) has been obtained from the reaction of tri(2-pyrrolyl)methane with phosphorus trichloride, in the presence of triethylamine. This compound is stable to methanolysis, hydrolysis, and aerial oxidation at room temperature. Phosphorylation of various 1,2,4-triazoles with halophosphines has given a route to the heterocyclic system (110), and routes to various [2,4,l]benzodiazaphosphinines, e.g., (Ill), have also been developed. ... 

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. 

Diphenylmethyl bromide allowed to react 5 hrs. at room temp, with triethylamine-borane complex in nitromethane -> diphenylmethane. Y ca. 100%. - The yields depend on the stability of the carbonium ions derived from the halides. Prim, halides can not be reduced by this method. F. e., also in liq. SO2, s. S. Matsumura and N. Tokura, Tetrah. Let. 1968, 4703 with diborane in nitromethane s. Tetrah. Let. 1969, 363. 

Aminophosphines. The synthesis and use of aminophosphines as ligands have been reviewed. Raeemie ehlorophosphines of the type R R PCl have been shown to react stereoselectively with chiral amines (1-phenylethylamine or aminoacid esters) in the presence of triethylamine to give the diastereomerically enriched aminophosphines (137), which were isolated as diastereomerically pure crystalhne borane complexes. This approach has also been used in the synthesis of chiral t-butylphenylphosphine oxide, via the acid hydrolysis of an intermediate chiral aminophosphine. Among other new mon-oaminophosphines prepared by treatment of primary or secondary amines with ehlorophosphines in the presence of a base are the adenine derivatives (138), the phosphinoalkylaminophosphines (139), " the aminophosphine-phosphine... 

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