Asymmetric Induction via a Helically Chiral Anion: Enantioselective Pentacarboxycyclopentadiene Brønsted Acid-Catalyzed Inverse-Electron-Demand Diels–Alder Cycloaddition of Oxocarbenium Ions

Abstract

An enantioselective catalytic inverse-electron-demand Diels-Alder reaction of salicylaldehyde acetal-derived oxocarbenium ions and vinyl ethers to generate 2,4-dioxychromanes is described. Chiral pentacarboxycyclopentadiene (PCCP) acids are found to be effective for a variety of substrates. Computational and X-ray crystallographic analyses support the unique hypothesis that an anion with point-chirality-induced helical chirality dictates the absolute sense of stereochemistry in this reaction.

Stereoselective Reactions of ortho-Quinone Methide and ortho-Quinone Methide Imines and Their Utility in Natural Product Synthesis

“…12,13 In 2017, the asymmetric cycloaddition of acyclic enamides to oQMs was achieved by Pan and coworkers using a BINOL-derived CPA catalyst. 14 A helically chiral pentacarboxypentadiene (PCCP) has also been shown by Lambert, Vetticatt, and co-workers 15 to be a potent catalyst for the generation and HDA reactions of oQMs with vinyl ethers (Scheme 4).…”

Reversibility and reactivity in an acid catalyzed cyclocondensation to give furanochromanes – a reaction at the ‘oxonium-Prins’ vs. ‘ortho-quinone methide cycloaddition’ mechanistic nexus

“…Intrigued by these mechanistic discrepancies and cognizant of both the increasing number of related Brønsted acid catalyzed reactions and the ambiguity that remains between a concerted o QM cycloaddition pathway and a stepwise carbocation-mediated alternative for a variety of reactions ( e.g. Scheme 2),2,10–14 we decided to investigate further.…”

Chiral Pentacarboxycyclopentadiene-Based Brønsted Acid-Catalyzed Enantioselective Desymmetrization of Meso-Epoxides by 2-Mercaptobenzothiazoles

“…12 Recently, Diels–Alder reactions between salicylaldehyde acetals and vinyl ethers catalyzed by a different PCCP catalyst were also reported. 13 Other groups have also reported transfer hydrogenations and preparations of chiral aminals using Lambert’s catalyst. 14 We believe that the development of PCCP-based chiral strong Brønsted acid catalyst could potentially alleviate some of the problematic issues for using BINOL-based chiral phosphoric acid derivatives.…”