Reduction with lithium triethylborohydride

The reduction with lithium triethylborohydride is far faster than that with sodium thiophenoxide, lithium aluminum hydride, or lithium borohydride. 

Chloroborepin (17) is readily converted to the corresponding Mo(CO)3 complex (Equation (4)) by reaction with tricarbonyl-tris(pyridine)molybdenum and BF3 Et20 in ether. This Mo(CO)3 derivative is smoothly converted to the corresponding 1 /f-borepin-molybdenum complex (18) by reduction with lithium triethylborohydride (Super-Hydride) in THF (Equation (5)). This is noteworthy as (18) cannot be prepared directly from the highly labile 1//-borepin itself <93AG(E)1065>. 

Complex hydrides have been used rather frequently for the conjugate reduction of activated dienes92-95. Just and coworkers92 found that the reduction of a,ft-unsaturated ketene 5,5-acetals with lithium triethylborohydride provided mixtures of 1,4- and 1,6-reduction products which were transformed into enals by treatment with mercuric salts (equation 27). Likewise, tetrahydro-3//-naphthalen-2-ones can be reduced with L-Selectride to the 1,6-reduction products93 -95 this reaction has been utilized in the stereoselective synthesis of several terpenes, e.g. of (/ )-(—)-ligularenolide (equation 28)95. Other methods for the conjugate reduction of acceptor-substituted dienes involve the use of methylcopper/diisobutylaluminum hydride96 and of the Hantzsch ester... 

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... 

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. 

The perhydro-isoxazolo[2,3-fl]pyridine system offers a route to 2,6-disubstituted piperidines. For example, the reaction between styrene and the substituted 3,4,5,6-tetrahydropyridine-l-oxide (69) gives the isoxa-zolidine (70) which, on benzylation, gives 71. This was subjected to reductive cleavage of the N—O bond with lithium aluminum hydride, followed by mesylation of the aminodiol produced. Treatment of the mesylate with lithium triethylborohydride gave the trans-2,6-disubstituted piperidine... 

Table 4 Reduction of Alkyl Halides with Lithium Triethylborohydride in THF ...

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. 

Aldols possessing a 2-(1-trimethylsilyl)vinyl substituent give high yields of the corresponding 1,2-syn reduction product with lithium triethylborohydride regardless of the substitution pattern at C-3. The same workers have demonstrated that removal of the silyl group from the C-2 vinylic substituent cleanly inverts the stereochemistry... 

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). 

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