Sulfonyl-stabilized oxiranyllithiums

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. ... 

Related Reagents. Optically active trisubstituted sulfonyl-stabilized oxiranyllithiums can be generated by deprotonation of the corresponding epoxy sulfones (eq 9). Due to the diminished reactivity of the reagents by steric hindrance, the reaction with triflates requires HMPA to obtain a high yield of product (eq 10). ... 

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