Boron-stabilized reactions with epoxides

While alkylation of sulfonyl-stabilized oxiranyllithiums with primary alkyl triflates proceeds in high yield, the reaction towards epoxides is relatively slow ( 2 h) and the decomposition of oxiranyllithium is marked, such that it decreases the yield, especially in the case of a Z-isomer (eq 7 and 8). Addition of boron trifluoride diethyl etherate promotes this epoxide-epoxide coupling reaction. One of the diastereoisomers of eq 8 has been elaborated via 5-endo cyclization into a marine tetrahydrofuran isolated from a brown alga. ... 

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