Enantioselective Palladium‐Catalyzed Carbonylative Carbocyclization of Enallenes via Cross‐Dehydrogenative Coupling with Terminal Alkynes: Efficient Construction of α‐Chirality of Ketones

Abstract

An enantioselective Pd /Brønsted acid-catalyzed carbonylative carbocyclization of enallenes ending with a cross-dehydrogenative coupling (CDC) with a terminal alkyne was developed. VAPOL phosphoric acid was found as the best co-catalyst among the examined 28 chiral acids, for inducing the enantioselectivity of α-chiral ketones. As a result, a number of chiral cyclopentenones were easily synthesized in good to excellent enantiomeric ratio with good yields.

Palladium-catalyzed oxidative dehydrogenative carbonylation reactions using carbon monoxide and mechanistic overviews

“…Moreover, the Bäckvall group found that, under the catalysis of Pd II and VAPOL phosphoric acid (CPA), the asymmetric version of the dehydrogenative carbonylation-carbocyclization reaction was realized to afford ketones bearing a-chirality from enallenes (Scheme 25). 33 Vaulted biaryl-type chiral phosphoric acids served as useful co-catalysts for this asymmetric transformation, therefore ketone products were generated in good yields with up to 95.5 : 4.5 e.r. In the catalytic cycle, enantioselective migratory insertion of the olefin into the C-Pd bond produces the carbocyclic intermediate Int-20, introducing the chirality at the a-position of the ketone.…”

Palladium‐Catalyzed Cascade Cyclization/Alkynylation Reactions

“…After many attempts, Bäckvall and co‐workers demonstrated a enantioselective Pd/VAPOL phosphoric acid‐catalyzed asymmetric dehydrogenative cascade alkynylation reaction of enallenes ( 63 ) with terminal alkynes for the preparation of α‐chirality ynones ( 64 ) (Scheme ) . The authors found that chiral phosphoric acids were proven to be the superior ligands, while other types of ligands failed to give any cyclized product or resulted in low enantioselectivity.…”

“…Based on the obtained results and previous literaturep recedents, the authors described the palladium-catalyzed oxidative cascade alkynylation reactiona sf ollowing (Scheme After many attempts, Bäckvall andc o-workersd emonstrated ae nantioselective Pd/VAPOL phosphorica cid-catalyzed asymmetric dehydrogenative cascade alkynylation reaction of enallenes (63)w ith terminal alkynes for the preparation of a-chirality ynones (64)( Scheme 33). [64] The authors found that chiral phosphoric acids were proven to be the superior ligands, while other types of ligands failed to give any cyclized product or resulted in lowe nantioselectivity.E mploying pre-made Pd II -VAPOL phosphate complex as the catalytic system in PhCl at 0 8Cc onditions, as eries of chiral ynones were successfully obtained in ah ighly stereoselective manner. However,t he poor yield and ee value were observedw hen substituents at the olefin moiety were investigated under the optimized reaction conditions.…”

Polycyclic Compounds from Allenes via Palladium-Mediated Intramolecular Carbopalladation/Nucleophilic Substitution Cascade Processes

“…[18][19][20][21] Amongst the chemical transformations of allenes, transition-metal-promoted reactions are of particular interest. [22][23][24][25][26][27][28][29][30][31] Generally, transition-metal derivatives can react with allenes in two ways: As a Lewis acid they can coordinate either double bond, usually the less hindered one, and activate it for further transformations, or, upon coordination, carbometallation can occur creating a novel organometallic species that can undergo further transformations. Regarding the first pathway, a large number of structures have been reported where the allene acts as an η 2 ligand (Scheme 1, structure a), however, the substituents can significantly influence the shape of the intermediate, which can have several other forms (Scheme 1, structures b, c and d), as exemplified by well-studied Au species.…”