Intermolecular [2+2] Reaction of N‐Allenylsulfonamides with Vinylarenes: Enantioselective Gold(I)‐Catalyzed Synthesis of Cyclobutane Derivatives

Abstract

Ein Hauch von Gold: N‐Allenylsulfonamide reagieren bei −70 °C mit Styrolderivaten in hohen Ausbeuten und Enantioselektivitäten zu chiralen Cyclobutanen. Phosphoramidit‐Liganden wie 1 vermitteln diese asymmetrische Gold(I)‐katalysierte [2+2]‐Cycloaddition. Tf=Trifluormethansulfonyl.

The Future of Catalysis by Chiral Lewis Acids

“…An intramolecular carbonyl-ene reaction has also been shown to produce polycyclic products in high yield and stereocontrol Scheme 27 Intermolecular [2+2] reaction of N-allenyl sulfonamides with vinyl arenes [125] The Future of Catalysis by Chiral Lewis Acids that were previously formed by cationic polyene cyclization (Scheme 31), thus opening a new synthetic methodology for the stereoselective synthesis of polycyclic compounds [137].…”

“…Highly polarized ynamide reactions with cyclic enones (the Ficini reaction), catalyzed by a chiral ruthenium(II)-PNNP catalyst, produce amidocyclobutenes in high yield with high enantiocontrol [123], and a chiral iridium catalyst has been reported to form cyclobutene products from reactions of arylacetylenes with norbornadiene derivatives [124]. Allenamide cycloadditions with alkenes that are catalyzed by gold(I) [125,126] have added to the versatility of this methodology for the formation of cyclobutane compounds; these reactions presumably occur in a stepwise fashion involving initial activation of the allene by the gold(I) catalyst and subsequent attack by the alkene that, as shown in Scheme 27 [125], can achieve high enantiocontrol. The carbonyl-ene reaction is a versatile, atom-economical process for the construction of carbon-carbon bonds to generate homoallylic alcohols that has generated considerable interest as a result of asymmetric catalysis of this transformation [127].…”

Gold(I)‐Catalyzed Bis‐Alkynylation Reaction of Aromatic Aldehydes with Alkynylsilanes

“…On the basis of our ongoing research program in gold catalysis [7] and the acquired experience in iodonium-mediated activation of C À C unsaturations for reaction discovery, [8] we were intrigued about the possibility of timely developing an entirely gold-based approach to achieve this demanding aldehyde bi-functionalization process, which ultimately relies on the catalytic and consecutive creation of two C À C bonds in one synthetic operation. [9] Considering the conceptual frame graphically outlined in Scheme 2, we reasoned that tuning the nature of the electrophilic metal would allow execution of this tandem process on the exclusive basis of gold catalysis.…”

Gold(I)‐Catalyzed Cascade Cycloadditions between Allenamides and Carbonyl‐Tethered Alkenes: An Enantioselective Approach to Oxa‐Bridged Medium‐Sized Carbocycles

“…[2] In this context, we and others have reported several intramolecular goldcatalyzed cycloadditions involving allenes, [3] as well as intermolecular cycloadditions of allenamides to dienes, (4+2), or to alkenes, (2+2). [4,5] The high regioselectivity observed in the (2+2) annulations, [5a] together with the intrinsic requirement of a carbocation-stabilizing group at the alkene, suggests that this reaction proceeds through a cationic pathway such as that depicted in the Scheme 1 (upper). [6] In light of this mechanism, we envisioned that interception of the carbocationic intermediate II by an internal nucleophile might result in the assembly of interesting bicycles through the cationic cascade shown in the Scheme 1 (bottom).…”