Preparation and reactions of 3‐oxa‐ 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‐hexenyllithium and a variety of 4‐oxa‐5‐hexenyllithiums. The 3‐oxa system is inherently unstable and fragments via facile β‐elimination to give the anion of allyl alcohol and ethylene. The 4‐oxa‐5‐hexenyllithiums, in contrast, are stable at low temperatures but undergo novel isomerization upon warming to deliver the lithium salt of a 4‐alken‐1‐ol in the formal equivalent of an unprecedented [1,4]‐Wittig rearrangement. The rearrangement 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.