Lithium butylborohydride

Reduction of unsaturated ketones to unsaturated alcohols is best carried out Nit v complex hydrides. a,/3-Unsaturated ketones may suifer reduction even at the conjugated double bond [764, 879]. Usually only the carbonyl group is reduced, especially if the inverse technique is applied. Such reductions are accomplished in high yields with lithium aluminum hydride [879, 880, 881, 882], with lithium trimethoxyaluminum hydride [764], with alane [879], with diisobutylalane [883], with lithium butylborohydride [884], with sodium boro-hydride [75/], with sodium cyanoborohydride [780, 885] with 9-borabicyclo [3.3.1]nonane (9-BBN) [764] and with isopropyl alcohol and aluminum isopro-... 

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. 

The first asymmetric synthesis of (-l-)-abresoline was achieved from the chiral piperidine derivative 153, which upon treatment of its hydroxy side-chain substituent with carbon tetrabromide, triphenylphosphine, and triethyl-amine cyclized to the frarcr-quinazolidine 154. Deketalization and silyl protection of the phenolic group, followed by stereoselective reduction with lithium tri-t -butylborohydride (L-Selectride ), gave an alcohol, which after acylation and deprotection furnished (-l-)-abresoline 155 (Scheme 25) <2005TL2669>. 

Although sodium borohydride appears to be the most popular reducing agent, a significantly better endo selectivity was achieved in the reduction of bicyclo[3.2.0]hept-2-en-6-ones using lithium tri-fer -butoxyaluminum hydride instead, e.g. formation of 3.251 In another study,99 lithium tri-sec-butylborohydride was found to reduce (la,4a,5a)-4-benzy)oxycarbonyl-2-oxabi-cyclo[3.2.0]heptan-6-one to (la,4oc,5a,6/i)-4-benzyloxycarbonyl-2-oxabicyclo[3.2.0]heptan-6-ol (4) with complete stereoselectivity. 

Optically pure 1,2-diols.1 The acyllactones 1, obtained by reaction of a Grig-nard reagent with the acid chloride derived from (R)-( -)- or S-( + )-glutamic acid, are reduced by lithium tri-sec-butylborohydride almost exclusively to syn-alcohols (2), regardless of the nature of the R group. In contrast, reduction of 1 with sodium... 

Stereoselective acyclic enolization2 This reaction can sometimes be achieved by conjugate reduction of acyclic a,(3-enones by lithium tri-sec-butylborohydride (1). When an enone reacts with 1 mainly by 1,2-reduction Li/NH3 can be used for conjugate reduction. In at least one case reduction with 1 is more stereoselective than that with Li/NH3. The stereoselectivity in general can be correlated with conformational preferences of enones.3... 

Enol triflatesfrom affi-enones.1 The reaction can be carried out by conjugate reduction of the enone with lithium tri-sec-butylborohydride followed by reaction of the resulting enolate with N-phenyltriflimide. The method is generally useful, but 1,2-reduction can predominate in the case of (3,(3- or even y,y-disubstituted a,(3-enones. 

Oxidation reactions r-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 m-Chloroperbenzoic acid, 76 Reduction reactions Chlorodiisopinocampheylborane, 72 Diisobutylaluminum hydride-Tin(II) chloride- (S) -1 - [ l-Methyl-2-pyrrolidi-nyljmethylpiperidine, 116 Lithium borohydride, 92 Lithium tri-sec-butylborohydride, 21 B-3-Pinanyl-9-borabicyclo[3.3.1]-nonane, 249... 

SlLYL ENOL ETHERS Chiorotrimethylsilane-Zinc, 82 Lithium amides, chiral, 159 Lithium tri-sec-butylborohydride, 167 Organotin reagents, 211 Osmium tetroxide-Trimethylamine N-ox-ide-Pyridine, 223... 

Lithium dialkylcuprates-Boron trifluoride etherate, 208 Lithium dibutylcuprate-Boron trifluoride etherate, 208 Lithium dimethylcuprate-Boron trifluoride etherate, 208 Lithium tri-sec-butylborohydride, 21, 167, 248... 

Lithium n-butylborohydride, Li-rr-BuBH3. Mol. wt. 77.89. The reagent is prepared by reaction of n-butyllithium with borane-dimethyl sulfide. 

---