Lithium triethylborohydride reaction with epoxides

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... 

Reaction with a hindered epoxide.l The trans-epoxide (1) of tetramethyllimonene is inert to KOH (130°), LiAlH4 (THF, 90°), and even lithium triethylborohydride. It is opened by aluminum isopropoxide (110°) to give 70 30 mixture of 2 and 3. Reaction with LDA is more selective and gives 2 in 95% yield. In contrast, reaction with N-lithioethylenediamine (1, 567 570) gives 3 in 90% yield. The 70 30 mixture of 2 and 3 is converted by N-lithioethylenediamine to the more stable isomer 3. 

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. 

Epoxides can be reduced to alcohols. Lithium aluminum hydride effects reduction by nucleophilic attack, and hydride is therefore added at the less substituted carbon atom. Lithium triethylborohydride is more reactive than LiAlH4 and is superior for epoxides that are resistant to reduction." A good deal of work has been done on the reduction of epoxides with species generated from reaction of aluminum... 

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