Lithium triethylborohydride, reductive

For reasons of brevity we report only the principal four syntheses. Dibenzocyclooctene 67 was hydrogenated affording a mixture of two cis lactones (68) and (69) (the second one probably arises due to the isomerization of the double bond), Scheme (13). Reduction of the lactones lead to a single diol 70. Treatment with methanesufonyl chloride in pyridine followed by lithium triethylborohydride reduction completed the synthesis of (-)-wuweisizu C (71) [65],... 

However, the former method requires the troublesome manipulation involved in preparing sodium selenide (or lithium selenide) in liquid ammonia and conducting the silylation in benzene (or diethyl ether). The latter method is inefficient and results in a low yield of the desired disilyl selenide. Thus a one-pot, high-yield procedure based on the lithium triethylborohydride reduction of elemental selenium has been developed, as depicted in eq 3. In this method, both preparation of Li2Se and silylation with MesSiCl are performed in THE Technically important is the use of selenium shot if selenium powder is utilized, the yield of Li2Se decreases sharply. Moreover, addition of small amount of boron trifluoride etherate (1.6 mol %) accelerates the silylation of Li2Se. ... 

Lithium triethylborohydride reductions of tosylate derivatives of methyl 4,6-0-benzylidene-a-D-glucopyranoside were highly regio-selective and gave good yields of deoxy-sugars via epoxide intermediates thus, the 3-mono- and 2,3-dl-O-tosylates gave the same... 

Reductive cleavage of oxiranes to alcohols by lithium aluminum hydride is an important reaction (64HC(19-1)199), but the most powerful hydride donor for this purpose is lithium triethylborohydride (73JA8486). 

Lithium triethylborohydride is a superior reagent for the reduction of epoxides that are relatively unreactive or prone to rearrangement.169... 

Complex hydrides have been used rather frequently for the conjugate reduction of activated dienes92-95. Just and coworkers92 found that the reduction of a,ft-unsaturated ketene 5,5-acetals with lithium triethylborohydride provided mixtures of 1,4- and 1,6-reduction products which were transformed into enals by treatment with mercuric salts (equation 27). Likewise, tetrahydro-3//-naphthalen-2-ones can be reduced with L-Selectride to the 1,6-reduction products93 -95 this reaction has been utilized in the stereoselective synthesis of several terpenes, e.g. of (/ )-(—)-ligularenolide (equation 28)95. Other methods for the conjugate reduction of acceptor-substituted dienes involve the use of methylcopper/diisobutylaluminum hydride96 and of the Hantzsch ester... 

A simple and general method for the preparation of surfactant-free, thiol-functionalized iridium nanoparticles was reported by Ulman and coworkers in 1999 [11], The synthesis consisted of a reduction of the dihydrogen hexachloroiri-date (IV) H2lrCl6 H20 precursor by lithium triethylborohydride ( super-hydride ) in the presence of octadecanethiol (C18H37SH) in tetrahydrofuran (THF) (Scheme 15.1). The obtained iridium nanoparticles were crystaUine with fee (face-centered cubic) packing, and showed a wider size distribution with diameters ranging from 2.25 to 4.25 nm. 

Other reagents used for the preparation of lactones from acid anhydrides are lithium borohydride [1019], lithium triethylborohydride (Superhydride ) [1019] and lithium tris sec-butyl)borohydride (L-Selectride ) [1019]. Of the three complex borohydrides the last one is most stereoselective in the reduction of 3-methylphthalic anhydride, 3-methoxyphthalic anhydride, and 1-methoxynaphthalene-2,3-dicarboxylic anhydride. It reduces the less sterically hindered carbonyl group with 85-90% stereoselectivity and is 83-91% yield [1019]. 

Other reagents used for reduction are boranes and complex borohydrides. Lithium borohydride whose reducing power lies between that of lithium aluminum hydride and that of sodium borohydride reacts with esters sluggishly and requires refluxing for several hours in ether or tetrahydrofuran (in which it is more soluble) [750]. The reduction of esters with lithium borohydride is strongly catalyzed by boranes such as B-methoxy-9-bora-bicyclo[3.3.1]nonane and some other complex lithium borohydrides such as lithium triethylborohydride and lithium 9-borabicyclo[3.3.1]nonane. Addition of 10mol% of such hydrides shortens the time necessary for complete reduction of esters in ether or tetrahydrofuran from 8 hours to 0.5-1 hour [1060],... 

Good to excellent yields (62-90%) of alcohols were reported in reductions of dimethyl and diethyl amides of benzoic acid and aliphatic acids by lithium triethylborohydride (2.2 mol per mol of the amide) in tetrahydrofuran at room temperature [700, 7777]. 

Stereoselective reaction with ketones. The reaction of ketone 1 with methyl-lithium, trimethylaluminum, and lithium letramethylaluminate shows no stcrco-specificity. The reaction with mcthylmagncsium bromide gives the two possible adducts in the ratio 2.4 1. The best stereospccificity is observed with dimethylsulf-oxonium methylide, which converts 1 into 2 and 3 in a ratio about 5 1. Reduction of the epoxides with lithium triethylborohydride gives the desired tertiary alcohols. This reaction was used in a synthesis of ( ) stemodin (4).2... 

Numerous reducing agents were tried at this point unsuccessfully. For example, lithium aluminum hydride destroyed the substrate, whereas DIBAH or lithium borohydnde in THF and sodium borohydride in ethanol led to reduction of the quinoline system. On the other hand, both potassium borohydride (either with or without 18-crown-6) and zinc borohydride (with or without ethanol) produced no reaction at all. Lithium triethylborohydride resulted in de-methoxylation, and sodium borohydride in refluxing THF gave a 45% yield of diol 16 together with overreduced product. 

Lithium triethylborohydride (Super-Hydride) is a much more powerful reducing agent than lithium aluminium hydride. It is useful for the reductive dehalogenation of alkyl halides, but unlike lithium aluminium hydride does not affect aryl halides. It is available as solution in tetrahydrofuran in sealed containers under nitrogen. The solutions are flammable and moisture sensitive and should be handled with the same precautions as are taken with other organometallic reagents (see Section 4.2.47, p. 442). 

Generation in situ. Lipshutz2 recommends lithium triethylborohydride for reduction of Cp2ZrCl2 to 1, because the co-product is (C2H5)3B, a relatively weak... 

The aminocyclitol d-48 was synthesized from l-218 (Scheme 28).103 Since direct peroxyacid oxidation of the exo-methylene group of compound l-218 had been shown to give selectively the undesired /<-spiro epoxide,35 102 it was first converted into l-219, followed by oxidation with m-CPBA to give the desired x-spiro epoxide d-220 (80%). The alcohol d-221 obtained in 73% yield by reductive cleavage of epoxide d-220 with lithium triethylborohydride (LiBHEt3) in THF was formed as a 2 3 mixture of two alcohols. However, hydrolysis of d-221 with hydrochloric acid gave d-48 (94%), which was further characterized by conversion into the pentaacetyl derivative 222 (82%). 

---