Lithium tri-s-butylborohydride

Stereoselective reductions based on complexed borohydrides have also proved of value in many instances in particular they have been of use in the synthesis of epimeric cyclic alcohols. For example, the reduction of 4-t-butylcyclo-hexanone to the cis-alcohol [99.5%, arising from equatorial hydride ion attack (i)] is effected by L-Selectride (lithium tri-s-butylborohydride, cf. Section 4.2.49, p. 448), or LS-Selectride53 (lithium trisiamylborohydride, cf. Section 4.2.49, p. 448) but to the trans-alcohol [98%, arising from axial hydride ion attack (ii)] with lithium butylborohydride.54 The experimental details of these reductions are given in Expt 5.34. 

Hydride reductions of (7) can be controlled to give either the (R) or (5) secondary hydroxy compound with good selectivity by choice of the reducing agent. Lithium Tri-s-butylborohydride (L-Selectride ) provided the (5)-alcohol (according to Cram s chelate rule) and Diisobutylaluminum Hydride (DIBAL) gave the (R)-carbinol in excess (eq 7). The DIBAL results were rationalized in terms of the open-chain Comforth dipole model. ... 

Analogous alkylation with different electrophiles allows for easy variation of the shielding moiety. The corresponding 3-substituted derivatives have been prepared from either 3-hydroxyisobomeol after separation of the regioisomeric mixture or from 3-eAro-hydroxycamphor regioselectively after reduction with Lithium Tri-s-butylborohydride (L-Selectride). ... 

Enantiomerically pure carboxylic acids are routinely obtained from N-acylsultams by Hydrogen Peroxide assisted saponification with Lithium Hydroxide in aqueous THF. 4 Alternatively, transesterification can be effected under neutral conditions in allyl alcohol containing Titanium Tetraisopropoxide, giving the corresponding allyl esters which can be isomerized/hydrolyzed with Wilkinson s catalyst (Chlorotris(triphenylphosphine)rhodium(I)) in Et0H-H20. This provides a convenient route to carboxylic acids containing base-sensitive functionality. Primary alcohols are obtained by treatment with L-Selectride (Lithium Tri-s-butylborohydride) in THF at ambient temperature. ... 

Phenolic oxidation of the diphenolic amide 285 using potassium ferric (III) cyanide afforded (-l-)-iV-formyldibromonarwedine (286), which was reduced successively with lithium tri-s-butylborohydride (L-Selectride) and with LiAlH4 to afford ( )-261. Resolution of ( )-261 using rf-camphoric acid provided (-)- and (-l-)-galanthamines (261) through the camphanate derivatives 287 and 288 165) (Scheme 30). 

L-Selectride lithium tri-s-butylborohydride MCPBA m-chloroperoxybenzoic acid... 

Trialkyl borohydrides such as Lithium Tri-s-butylborohydride and Potassium Tri-s-butylborohydride are superior reagents for the chemoselective 1,4-reduction of enones. On the other hand, 1,2-reduction can be obtained by using NaBHj in the mixed solvent MeOH-THF (1 9), or with NaBHj in combination with CeCH or other lanthanide salts. ... 

The stereoselectivity for equatorial alcohols has been enhanced by using the system NaBEU-CenHwif///) Chloride, which has an even higher propensity for attack from the more hindered side, or by precomplexing the ketone on MontmoriBonite KIO clay. On the other hand, bulky trialkylborohydrides (see Lithium Tri-s-butylborohydride) are best suited for synthesis of the axial alcohol through attack from the less hindered face. 

Lithium tri-i-amylborohydride is a generally more stereoselective reducing agent than the earlier reported lithium tri-s-butylborohydride. Thus 3-methyl- and 4-t-butyl-cyclohexanones yield trans-3-methyl- and cis-4-t-butyl-cyclohexanol respectively, in greater than 99.5% isomeric purity. In most hydride reductions of... 

Brown recommends lithium tri-s-butylborohydride as an exceptionally stereoselective reducing agent, enzymatic selectivity being attained and occasionally surpassed. The conversion of a ketone into its metal enolate... 

Carbonyl Reactivity.—A new reagent, lithium tri-s-butylborohydride, is claimed to exhibit enzyme-like stereoselectivity in reduction of cyclic (and bicyclic) ketones. Reduction of 2-methylcyclohexanone at 0°C in THF for 30 min occurred quantitatively to give the less stable cis-alcohol with an epimeric purity of 99.3%. 3,3,5-Trimethylcyclohexanone was reduced to the trans-alcohol with 99.8% stereoselectivity and 3-methylcyclohexanone likewise with 85% stereoselectivity. Reduction of 4-methylcyclohexanone to the cis-alcohol occurs with 80.5% stereoselectivity correspondingly cis-4-t-butyl-cyclohexanol is produced with 93% isomeric purity, much higher than in previous cited procedures, and this figure rises to 96.5% when reaction is... 

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