Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

Abstract

An enantioselective aza-Piancatelli rearrangement has been developed using a chiral Brønsted acid based on pentacarboxycyclopentadiene (PCCP). This reaction provides rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks from readily available starting material and is operationally simple.

Retro-Aza-Piancatelli Rearrangement Triggered Cascade Reaction of Methyl Furylacrylates with Anilines to Access Cyclopenta[b]pyrrolidinones

“…The Piancatelli reaction, a rearrangement of furfuryl alcohols to multisubstituted cyclopentenones, enables the direct transformation of a heterocycle to a carbocycle via a furan ring opening-4π electrocyclization process. Given the prevalence of cyclopentane motifs in natural products and biologically active compounds, this reaction has attracted extensive attention from synthetic chemists. , Over these years, the original stoichiometric amount of acid-mediated oxa-Piancatelli reaction has been extended to a range of Lewis acid (LA) or Brønsted acid (BA) catalyzed aza- and carbo-Piancatellil reactions. − Recently, significant progress has also been achieved in the cascade Piancatelli reactions by using functionalized anilines or furfuryl alcohols, providing facile access to structurally diverse multicyclic compounds . Nevertheless, it is important to note that all these reactions have almost exclusively relied on furfuryl alcohols to generate the key furanoxonium ion intermediates via an acid-catalyzed dehydration process (Scheme a).…”

Recent Advances on Piancatelli Reactions and Related Cascade Processes

“…49 In 2019, Read de Alaniz described another Brønsted acid catalyzed system based on chiral pentacarboxycyclopentadiene (PCCP, Scheme 20). 50 These transformations generally involve a key chiral anion-controlled enantioselective 4 electrocyclization process, providing rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks in high yields with excellent enantio-and diastereoselectivities.…”

Pentacarboxycyclopentadienes in Organic Synthesis

“…To expand the range of catalysts for this reaction, chiral PCCP acid 12 was tested to fi nd that the reaction of furylcarbinol 79a with aniline 80a in the presence of this catalyst gave 4-aminocyclopentenone 85a with a yield of 78% and enantioselectivity of 65% (Scheme 31) [78]. At 30°C (ee 73%) and 22°C (ee 78%), the selectivity increased by the yield dropped, but it proved possible to increased by prolonging the reaction time from 48 to 120 h. Of the solvent, CH 2 Cl 2 was found to be the most suitable.…”