α-Vinylation of Ester Equivalents via Main Group Catalysis for the Construction of Quaternary Centers

Abstract

A methodology for the construction of sterically congested quaternary centers via the trapping of vinyl carbocations with silyl ketene acetals is disclosed. This main group-catalyzed α-vinylation reaction is advantageous as methods to access these congested motifs are limited. Moreover, β,γ-unsaturated carbonyl moieties and tetrasubstituted alkenes are present in various bioactive natural products and pharmaceuticals, and this catalytic platform offers a means of accessing them using simple and inexpensive materials.

Main Group-Catalyzed Cationic Claisen Rearrangements via Vinyl Carbocations

“…Inspired by the ability to generate allyl vinyl ethers through transition metal-catalyzed cross coupling reactions and the documented accelerating effects of charge in sigmatropic rearrangements, − we envisioned a strategy that could merge the two in a transition metal-free catalytic platform. Drawing on previous work, we hypothesized that generation of a high energy vinyl carbocation and subsequent reaction with weakly nucleophilic allyl ethers would generate a vinyl oxonium cation poised to undergo a charge-accelerated [3,3] sigmatropic rearrangement (Figure C). Utilizing Li + weakly coordinating anion (WCA) salts to ionize vinyl sulfonates, we began exploring the reactions of allyl ethers with vinyl tosylates in the presence of commercially available [Ph 3 C] + [B­(C 6 F 5 ) 4 ] − , which generates Lewis acidic [Li] + [B­(C 6 F 5 ) 4 ] − upon reaction with LiHMDS.…”