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

Abstract

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, 1,5allyl 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.

Achmatowicz Rearrangement-Inspired Development of Green Chemistry, Organic Methodology, and Total Synthesis of Natural Products

“…In a project directed to the construction of synthetically challenging 8-membered carbocycles through AchR and Prins cyclization (Scheme ), we unexpectedly observed a furan-derived byproduct, which was confirmed to be a 2,5-substituted furan . When compared with the starting furfuryl alcohol, this byproduct was deemed to be formed overall by a 1,5-allyl shift, a process that is forbidden through [3,5]-sigmatropic rearrangement on the basis of the Woodward–Hoffmann rule.…”

“…2022, 61, e202205919. 3 This work illustrates our exploration of the new reactivity/ transformation of Achmatowicz rearrangement products. While originally designed for the construction of 8membered carbocycles through Prins cyclization of Achmatowicz rearrangement products, we unexpectedly discovered a 1,5-allyl shift through an oxonia-Cope rearrangement and an unprecedented retro-Achmatowicz rearrangement, which offers a new way of synthesis for important and versatile 2-acyl-5-allylfurans.…”

“…New postrearrangement transformations are highly desirable for further applications of AchR in organic synthesis. In this context, we developed four types of transformations: reductive ring expansion, [3 + 2] cycloaddition with 1,3-dicarbonyls, palladium-catalyzed arylation, and unexpected 1,5-allyl shift (Scheme ). These new transformations open a new avenue to construct fully functionalized heterocycles.…”

“…In a project directed to the construction of synthetically challenging 8-membered carbocycles through AchR and Prins cyclization (Scheme 10), we unexpectedly observed a furan- derived byproduct, which was confirmed to be a 2,5substituted furan. 3 When compared with the starting furfuryl alcohol, this byproduct was deemed to be formed overall by a 1,5-allyl shift, a process that is forbidden through [3,5]sigmatropic rearrangement on the basis of the Woodward− Hoffmann rule. Different from the related well-established and widely used 1,3-or 1,2-allyl shift through Cope, Claisen, Carroll, and Sommelet−Hauser rearrangements, this new 1,5allyl shift involves sequential ring-expansion (AchR) and ringcontraction (unknown) rearrangement.…”

“…Int. Ed.202261e202205919 . This work illustrates our exploration of the new reactivity/transformation of Achmatowicz rearrangement products.…”