Lithium triethylborohydride epoxides

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

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... 

Reaction with a hindered epoxide.l The trans-epoxide (1) of tetramethyllimonene is inert to KOH (130°), LiAlH4 (THF, 90°), and even lithium triethylborohydride. It is opened by aluminum isopropoxide (110°) to give 70 30 mixture of 2 and 3. Reaction with LDA is more selective and gives 2 in 95% yield. In contrast, reaction with N-lithioethylenediamine (1, 567 570) gives 3 in 90% yield. The 70 30 mixture of 2 and 3 is converted by N-lithioethylenediamine to the more stable isomer 3. 

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%). 

Reductive cleavage of cyclic ethers This complex is effective for reductive cleavage of cyclic ethers. The order of reactivity is epoxide > oxetane > tetrahydrofurane>tetrahydropyrane>oxepane. It is less effective for cleavage of acyclic ethers, except for methyl ethers. The reaction involves formation of a complex of the ethereal oxygen with aluminum r-butoxide followed by Sn2 displacement with lithium triethylborohydride. Steric and electronic Victors are involved, but yields are >90% in favorable cases. 

Li[Et3BH] (Superhydride) (lithium triethylborohydride) Tetrahydrofuran -78 to RT ester —> alcohol ketone —> alcohol aldehyde —> alcohol alkyl halide —> alkane epoxide —> alcohol... 

Another modified metal hydride, lithium triethylborohydride, the so-called superhydride , has been introduced as a powerful reducing agent especially suitable for trisubstituted, tetrasubstituted and bicy-clic epoxides (Table 3). With trisubstituted epoxides the regiochemistry is completely controlled to give only tertiary alcohols. No skeletal rearrangement is observed for benzonorbomadiene oxide. 

Lithium triethylborohydride (LiEtjBH) is a super-nucleophile that reduces primary alkyl bromides " and tosylates more effectively to the corresponding hydrocarbons than does LiAlH4. Epoxides are readily cleaved to give alcohols by attack of the hydride at the less substituted carbon. ... 

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). 

Lithium triethylborohydride. CARBONYL COMPOUNDS Catechol-borane. Triethylsilane-Boron triflaoride. EPOXIDES Iron carbonyl. Methyltri-phenoxyphosphonium iodide. Sodium 0,0-diethyl phosphoiotelluioate. Tti-fluoroacetic anhydride-Sodium iodide. 

Epoxides can be reduced to alcohols. Lithium aluminum hydride effects reduction by nucleophilic attack, and hydride is therefore added at the less substituted carbon atom. Lithium triethylborohydride is more reactive than LiAlH4 and is superior for epoxides that are resistant to reduction." A good deal of work has been done on the reduction of epoxides with species generated from reaction of aluminum... 

Lithium triethylborohydride reducing agent, mild stereospecific reduction of epoxides... 

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... 

Several reducing agents have been utilized to remove tosylate esters of sugars and other polyols. In particular, lithium aluminum hydride and lithium triethylborohydride have been most extensively used [20-23]. When secondary alcohol tosylates are used, epoxide intermediates are frequently involved. Reduction is observed to occur through either C-0 or O-S bond cleavage [24]. In this chapter, we discuss our results from the reduction of 6-0-tosylates of D-glucal and D-galactal with lithium aluminum hydride in THF. 

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