UV light-driven asymmetric vinylogous aldol reaction of isatins with 2-alkylbenzophenones and enantioselective synthesis of 3-hydroxyoxindoles

Abstract

Chiral 3-hydroxyoxindoles are biologically important molecular motifs which frequently present in natural products and artificial compounds. Herein, we report an ultraviolet light-driven asymmetric vinylogous aldol reaction between versatile isatins and...

Tandem Vinylogous Aldol and Intramolecular [2 + 2] Cycloaddition toward Benzocyclobutenes by UV Light Photocatalysis

“…In accordance with the results of the control experiments and previous studies on the vinylogous aldol reaction, − a possible mechanism for this UV-light-catalyzed tandem reaction is proposed as shown in Scheme A. Initially, under the irradiation of UV LEDs, an intermolecular hydrogen atom transfer (HAT) process between methylbenzophenone 1 (methyl group) and isatin 2 (carbonyl group) occurs to afford radical intermediate IM1 and radical intermediate IM2 .…”

Light‐Mediated Aminocatalysis: The Dual‐Catalytic Ability Enabling New Enantioselective Route

“…UV light-driven enantioselective vinylogous aldol reaction using chiral thiourea catalyst. [28] glycine A11 provided the required activation to the ketone moiety 78 to form α-alkylating products 80.…”

“…In 2021, He and Han et al illustrated chiral amine-derived thiourea A10 catalyzed asymmetric vinylogous aldol reaction by reacting isatins 74 and 2-alkylbenzophenones 73 under ultraviolet light irradiation (Scheme 19a). [28] Mechanistic proposal by the authors disclosed that the crucial role of UV LEDs promoted 2-alkylbenzophenone 73 into its excited state, underwent a 1,5-hydrogen shift to form a transient ortho-quinonedimethide (o-QDM) 76 a. On the other hand, thiourea A10 activates the isatin moiety 74 through hydrogen bonding and participated in a stereoselective nucleophilic addition with in situ generated o-QDM intermediate to deliver aldol product 75 (Scheme 19b).…”

“…In 2021, He and Han et al. illustrated chiral amine‐derived thiourea A10 catalyzed asymmetric vinylogous aldol reaction by reacting isatins 74 and 2‐alkylbenzophenones 73 under ultraviolet light irradiation (Scheme 19a) [28] …”

NickelII-catalyzed asymmetric photoenolization/Mannich reaction of (2-alkylphenyl) ketones

“…Later, Melchiorre creatively realized the enantioselective PEDA reaction with maleimides by using a cinchona-thiourea catalyst, 8 and Gao's group took the PEDA reaction as a key step catalyzed by Ti–TADDOL complexes in asymmetric synthesis of natural products. 9 In addition to dienophiles, other reaction partners to trap the ephemeral photoenols enantioselectively have been exploited, such as in the Michael reaction 10 and aldol 11 and allylic alkylation-type reactions. 12 By contrast, the catalytic asymmetric photoenolization/Mannich reaction (PEM) seemed to encounter challenges such as: (1) the irrepressible background reaction and (2) the potential epimerization of the product due to its further photoenolization.…”