Lithium triethylborohydride tosylates

An oven-dried 300-ml flask, equipped with a side-arm fitted with a silicone rubber septum, a magnetic stirrer bar, and a reflux condenser connected to a mercury bubbler, is cooled to room temperature under a stream of dry nitrogen. Tetrahydrofuran (20 ml) is introduced, followed by 7.1 g (25 mmol) of cyclooctyl tosylate (1). The mixture is cooled to 0 °C (ice bath). To this stirred solution, lithium triethylborohydride (Section 4.2.49, p. 448) [33.3 ml (50 mmol) of a 1.5 m solution in tetrahydrofuran] is added, and the ice bath removed. The mixture is stirred for 2 hours (c. 25 °C). Excess hydride is decomposed with water. The organoborane is oxidised with 20 ml of 3 m sodium hydroxide solution and 20 ml of 30 per cent hydrogen peroxide [(2) and (3)]. Then the tetrahydrofuran layer is separated. The aqueous layer is extracted with 2 x 20 ml portions of pentane. The combined organic extracts are washed with 4 x 15 ml portions of water to remove ethanol produced in the oxidation. The organic extract is dried (MgS04) and volatile solvents removed by distillation (2). Distillation of the residue yields 2.27 g (81%) of cyclooctane as a colourless liquid, b.p. 142-146 °C, Wq0 1.4630. 

Other useful nucleophiles for the ring opening of aziridines include bromide, as shown in the Amberlyst-15 catalyzed reaction of lithium bromide with vinyl aziridine 167 <02TL5867> and hydride, which can be delivered by lithium triethylborohydride. This is illustrated by the conversion of tosyl azabicyclo[3.1.0]hexene 169 to the corresponding protected cyclopentenyl amine (170) in 79% yield <02TL723>. 

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). 

Several methyl 6-deoxy-hexopyranoside 2- and 4-tosylates undergo rearrangement to branched-chain sugars on treatment with lithium triethylborohydride, e.g. (37)—a(38) and (39)-+(40)Methyl 6-deoxy-2,3-di-O-tosyl-o(-D-galactopyranoside yielded both a 3-deoxy-... 

Efficient deoxygenation of 2 - or 3 -O-tosyl-adenosine with concomitant adjacent epimerization to yield threo-deoxypentose derivatives on treatment with lithium triethylborohydride (Scheme 4) ... 

Lithium triethylborohydride continues to be a useful synthetic reagent. It has been reported that this reagent in THF reduces the toluene-p-sulphonates of primary and secondary alcohols to the corresponding alkanes. The reduction is even applicable to tosylates of cycloalkanols, hindered alcohols, and polyhydroxy derivatives. The reaction of lithium triethylborohydride with elemental sulphur has been reported to form rapidly Li aS or Li aS a (depending upon the stoicheiometry), which can then be used to prepare sulphides, RaS, and disulphides, RaS a, in high yield. Similarly, the publication of a convenient... 

Several methods for the reduction of allylic functional groups have been reported. Although some of these are derivative of earlier procedures, useful improvements and modifications are noteworthy. For example, combination of [Pd(PhaP)4] with lithium triethylborohydride provides an effective system for the reductive removal of allylic ethers, sulphides, sulphones, selenides, and t-butyl-dimethylsilyl ethers. Many of these functional groups, of course, are not readily removed by other methods. Furthermore, this combination gives good to excellent maintenance of the regio- and stereo-integrity of the allylic double bonds. In a similar fashion, 2-tosyl homoallyl alcohols can be easily desulphonylated to... 

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... 

Lithium triethylborohydride has been shown to be an excellent reagent for the rapid reduction of alcohol tosylates to alkanes, even in hindrred cases. A comparative study on cyclohexyl tosylate marked out this reagent or the 9-BBN derivative (45) as the reagents of choice, but LiEtsBH is more readily available. 

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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