Lithium triethylborohydride ketones

Diphenyl telluropyran-4-one (typicalprocedure)7° 120 mL (0.12 mol) of a 1.0 M solution of lithium triethylborohydride in tetrahydrofuran are added to 7.65 g (60 mmol) of powdered tellurium under nitrogen, and the mixture stirred at 20°C for 4 h. A solution of sodium ethoxide (prepared from 5.52 g (0.24 mol) of sodium and 240 mL of absolute alcohol) is added to the dilithium telluride, 13.8 g (60 mmol) of bis(phenylethynyl) ketone are dissolved in a mixture of 150 mL of tetrahydrofuran and 150 mL of 1 M sodium ethoxide in ethanol this solution is poured as quickly as possible into the deep-purple-coloured dilithium telluride soluhon. The flask containing the reaction mixture is immediately placed in a water bath at 50°C and the temperature slowly increased over 30 min until ethanol begins to condense on the side of the flask. The water bath is removed and the mixture is stirred overnight at 20°C. Dichloromethane (400 mL) is then added, the resultant mixture is washed with 800 mL of water, and the organic phase is separated and concentrated to an oil. The oil is dissolved in 600 mL of dichloromethane, and the solution is filtered through a pad of sand. The filtrate is washed with 200 mL of 2% aqueous sodium chloride soluhon, dried with anhydrous sodium sulphate, filtered and evaporated. The brownish solid residue is triturated with 20 mL of butanenitrile and the fine yellow solid is collected by filtration yield 10.9 g (51%) m.p. 126-129°C (from acetonitrile). 

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... 

Diastereoselective aldol reaction. Alkyl trityl ketones (2) are readily prepared by reaction of 1 with an aldehyde followed by Cr03 oxidation (50-70% overall yield). Because of steric effects these ketones undergo highly diastereoselective aldol condensation to give syn-adducts (95-99% syn). After protection of the hydroxyl group, the adduct is cleaved by lithium triethylborohydride.1... 

In unpublished work, Gribble and Obaza-Nutaitis (60) have adapted the Saul-nier-Gribble ellipticine synthesis (61) to the synthesis of olivacine (Scheme 14). Keto lactam 85, available from indole in four steps (71% yield) (61), was treated sequentially with methyllithium and lithium triethylborohydride to give diol 86, which, without isolation, was reduced with sodium borohydride to give 1-de-methylolivacine (87). This had been previously converted to olivacine (4) by Kutney and co-workers (62). The success of this synthesis of 87 was due to the fact that Saulnier and Gribble (63) had previously established that the ketone carbonyl of keto lactam 85 is more reactive than the lactam carbonyl group. 

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

The requirement for a powerful nucleophilic hydride reagent able to reduce even very hindered ketones rapidly and quantitatively has been satisfied by lithium triethylborohydride which was screened against selected representative functional groups. The quest for increased chemoselectivity in total synthesis has led to the development of reducing agents that will discriminate between various classes of ketone or between ketones and other carbonyl groups. 

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. 

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

Locher and Seebach have shown that lithium acetylides undergo 1,4-addition to l,l,l-triphenyl-3-penten-2-one (191), and the resulting acetylenic trityl ketones (192) are smoothly cleaved to acetylenic alcohols (193) by lithium triethylborohydride. ... 

Lithium hydride, prepared in an activated form according to equation (3), has been shown to reduce esters, aldehydes, and ketones to alcohols in the presence of equimolar vanadium (ill) chloride." Lithium hydride can also be used to prepare lithium triethylborohydride [equation (4)], and full details of... 

Lhommet and coworkers prepared the chiral bicyclic carbamate 1189 from L-lysine by a method that involved an electrochemical methoxylation (Scheme 150). ° This precursor, in effect a disguised acyliminium ion, reacted with the sdylated enol 1190 and trimethylsilyl triflate to give a diaste-reomeric mixture of p-keto esters (+)-1191, hydrolysis and decarboxylation of which produced ketone (—)-1192 as the only discernible product. It was essential to reduce this ketone stereoselectively in order to set up the configuration of the target alkaloid s side chain correctly. Fortunately, this was achieved with either K-Selectride or with lithium triethylborohydride. 

Lithium borohydride, 92 (lR,2S)-N-Methylephedrine-0-pro-pionate, 308 Norephedrine, 200 2-Oxazolidones, chiral, 225 (2R,4R)-Pentanediol, 237 Potassium triethylborohydride, 260 Other hydroxy carbonyl compounds (R)-( + )- and (S)-( - )-2,2 -Bis-(diphenylphosphine)-1,1 -binaphthyl, 36 Ketones... 

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