Science of Synthesis

Rück-Braun, K.; Freysoldt, T., Science of Synthesis, (2007) 35, 512.

Boron bromides are well-known reagents for ether cleavage. The strong Lewis acidity of boron tribromide can lead to cleavage of sensitive groups. A number of substituted bromoboranes of lower reactivity such as bromobis(dimethylamino)-[‌46‌] and bromo(dimethyl)borane[‌47‌] react with epoxides ‌38‌ to form bromo alcohols ‌39‌ and ‌40‌ (‌Scheme 16‌).[‌46‌–‌48‌] The milder conditions result in lower reactivity, but higher selectivities are achieved compared to boron tribromide. In addition, the use of boron bromide and dibromide–dimethyl sulfide complexes allow the mild, regio- and stereoselective ring opening of epoxides ‌38‌.[‌48‌] All transformations take place in nonaqueous media and are applicable even in the presence of acid- and base-labile groups (‌Scheme 16‌). This reaction has also been used on small natural product derivatives.[‌47‌]

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