Oxiranyllithium reagents

Oxiranyllithium reagents. Epoxides stabilized by a silyl group can be lithiated at the activated position (7, 45-46), but lithiation of nonstabilized epoxides results... 

Handling, Storage, and Precautions the oxiranyllithium is very unstable, even at —100 °C under argon, and should be reacted with electrophiles immediately. The reagent is also conforma-tionally unstable and slowly isomerizes to the trans-isomer when addition of an electrophile is delayed (about 5% isomerization after 20 min at -100 °C). Elevated temperatures (>—78 °C) cause rapid decomposition. - ... 

Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemi-... 

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). ... 

Reiterative application of this protocol has allowed the stere-ocontrolled construction of polytetrahydropyrans and polycyclic ethers containing six- and seven-membered rings (eq 5). Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemibrevetoxin B (eq 6). It is noteworthy that deprotonation of 1 by n-BuLi is much faster than butyl addition to the aldehyde. 

Asymmetric epoxides (64) and alcohols (65) have been synthesized from sulflny-loxiranes (63) via oxiranyllithiums and oxiranyl Grignard reagents which bear a carbanion-destabilizing alkyl group (Scheme 10). ... 

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