Chemoselectivity in Pd-Based Dyotropic Rearrangement: Development and Application in Total Synthesis of Pheromones

Abstract

In the dyotropic rearrangement of molecules with semiflexible structures, characterized by a freely rotating static C–C bond, the formation of a mixture of products is common due to the coexistence of several energetically comparable conformers. Herein, we report that it is possible to modulate the shifting groups by adjusting the metal’s coordination sphere in Pd-based dyotropic rearrangement. In the presence of a catalytic amount of Pd(II) salt, the reaction of γ-hydroxyalkenes or γ,δ-dihydroxyalkenes with Selectfluor affords fluorinated tetrahydropyranols or 6,8-dioxabicyclo[3.2.1]octanes (DOBCO), respectively. In this domino process, two C(sp²) and one allylic C(sp³) are sequentially activated and functionalized through a pivotal conformation-controlled chemoselective C(sp³)–C(sp³) and C(sp³)–Pd(IV) bond metathesis reaction. Mechanistic studies suggest a reaction sequence including 5-exo-trig oxypalladation, Pd oxidation, and chemoselective ring expansion 1,2-Csp³/Pd(IV) dyotropic rearrangement, followed by hydroxypalladation of in situ generated dihydropyrans. These findings provide a unique retrosynthetic disconnection for the synthesis of 6,8-DOBCO. We showcase its potential by developing a concise synthesis of three important pheromones. Notably, (+)-frontalin is synthesized from a commercially available 1,5-diene in only two steps, utilizing Sharpless catalytic asymmetric dihydroxylation and Pd-catalyzed domino cyclization developed in this study.