Sodium triethylborohydride reduction

Chemical routes involving the use of tungsten salts have been reported. W2C was claimed to be formed by the pyrolysis of an organometallic complex containing cyclopentadiene and carbonyl groups.8 The W2C formed was useful for ceramic applications such as wear resistant surfaces and cutting tools. The same phase was also prepared by the reduction of WC14 with sodium triethylborohydride.9 The material was formed as 1-5 nm-sized crystallites as shown by SEM and TEM. 

The reductive ring opening of 330a with sodium cyanoborohydride/titanium tetrachloride in acetonitrile occurs with no ester reduction whatsoever to provide 421 in 83% yield. Subsequent conversion to the tosylate followed by reduction with lithium borohydride/lithium triethylborohydride affords in 61% yield the crystalline diol 422. Lithium aluminum hydride or sodium borohydride reduction of the tosylate of 421 fails to produce clean reductions to 422. Epoxide ring closure of 422 is achieved with two equivalents of sodium hydroxide in methanol to fiimish in 93% yield (2 S, 3i )-2-benzyloxy-3,4-epoxybutan-l-ol (423) [140] (Scheme 94). 

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. ... 

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],... 

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. 

The reduction with lithium triethylborohydride is far faster than that with sodium thiophenoxide, lithium aluminum hydride, or lithium borohydride. 

The sex pheromone structure, 10-methyl-2-tridecanone, was synthesized using the carboxyl group as the source of the methyl branch (lA) (Figure 6). Undecylenic acid was a-propylated and resolved via amides. The procedure followed allowed us to obtain the alcohols,(R)- and (S)-2-propyl-10-undecenol (>99.6% ee). The corresponding bromide was reduced with lithium triethylborohydride (15) then the double bond was converted to a methyl ketone by a) oxymercuration, b) reduction of the C-Hg bond with sodium borohy-dride, and c) oxidation with dichromate. The male southern corn rootworm responds only to the (R)-configuration no biological activity was noted for the (S)-enantiomer. Therefore, in this instance the racemic compound would be predicted to monitor this species adequately. 

Ring cgntractions have been recorded in reductions and displacements of sulphonate esters. Treatment of the 6-deoxy-ditosylate (57) with lithium triethylborohydride gave the furanose (58), as well as the 3-reduced pyranoses (59) and (60), which arose via the mechanisms in Scheme 7. Substantial amounts of the DL-digino-furanoside (61) and the DL-rhodinofuranoside (62) were obtained by reaction of sodium benzoate in DiMF with the 4.-0-fflesylates of DL-... 

For reduction, lithium borohydride [38] has an advantage over sodium boro-hydride, as it is readily soluble in simple ether solvents. Lithium borohydride reduces selectively the esters in the presence of other reducible groups. The reduction of esters proceeds smoothly but relatively slowly. However, it is found [39] that in the presence of 10 mol% of lithium-9-boratabicydo[3.3.1]nonane, Li 9-BBNH, or lithium triethylborohydride, LiEtjBH strongly catalyzes the reduction of esters by lithium borohydride in diethyl ether. Catalytic effects have also been observed with B-OMe-9-BBN, LiB(OMe)2-9-BBN, and LiEt3BOMe (Table 25.12) [39]. 

Reduction. A variety of metal hydride reducing agents can be employed to reduce jr-allylpalladium dimers. These include sodium borohydride, sodium cyanoborohydride, lithium triethylborohydride, lithium aluminum hydride, lithium tri-ferf-butoxyaluminum hydride, polymethylhydrosiloxane, and RsSiH (eq Formic acids and formate salts also reduce... 

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