PREPARATION AND REACTIONS OF 3-OXA-5-HEXENYLLITHIUMS AND 4-OXA-5-HEXENYLLITHIUMS

Low-temperature lithium-iodine exchange between tert-butyllithium and the appropriate iodide has been used to generate 3-oxa-5-hexenyllithiu m and a variety of 4-oxa-5-hexenyllithiums. The 3-oxa system is inhere ntly unstable and fragments via facile beta-elimination to give the an ion of allyl alcohol and ethylene. The 4-oxa-5-hexenyllithiums, in con trast, are stable at low temperatures but undergo novel isomerization upon warming to deliver the lithium salt of a 4-alken-1-ol in the form al equivalent of an unprecedented [1,4]-Wittig rearrangement. The rear rangement is most likely mediated by 5-exo-trig ring closure of the 4- oxa-5-hexenyllithium to a (2-tetrahydrofuranyl)methyllithium followed by rapid opening to the alkoxide.