Asymmetric Induction and Simple Diastereoselectivity in the [2,3] Wittig Rearrangement of Ester Enolates

The [2,3] Wittig rearrangements of the lithio enolates of the cis‐configurated allylic ethers 5a–d are stereoselective. The tert‐butyl ester 5d gives 79% of a single rearrangement product 6d. The chiral center of the dioxolane controls the configuration at one of the newly formed stereogenic centers through asymmetric induction. The size of the dioxolane is responsible for the concomitant high syn selectivity. The [2,3] Wittig rearrangements of the trans‐configurated allyl esters 20a–d exhibit moderate stereocontrol through asymmetric induction; the ratio of syn (6) and anti products (21) can be tuned from 2:1 as in the case of the tert–butyl ester, to 1:3 by choosing the methyl ester.