1,5‐Allyl Shift by a Sequential Achmatowicz/Oxonia‐Cope/Retro‐Achmatowicz Rearrangement.

1,3‐Allyl and 1,2‐allyl shifts through [3,3]‐ and [2,3]‐sigmatropic rearrangements are well‐established and widely used in organic synthesis. In contrast, 1,5‐allyl shift through related [3,5]‐sigmatropic rearrangement is unknown because [3,5]‐sigmatropic rearrangement is thermally Woodward–Hoffmann forbidden. Herein, we report an unexpected discovery of a formal 1,5‐allyl shift of allyl furfuryl alcohol through a 2‐step sequential rearrangement. Mechanistically, this formal 1,5‐allyl shift is achieved through a sequential ring expansion/contraction rearrangement: 1) Achmatowicz rearrangement (ring expansion), and 2) cascade oxonia‐Cope rearrangement/retro‐Achmatowicz rearrangement (ring contraction). This new 1,5‐allyl shift method is demonstrated with >20 examples and expected to find applications in organic synthesis and materials chemistry. [ABSTRACT FROM AUTHOR]