Merging Gold/Copper Catalysis and Copper/Photoredox Catalysis: An Approach to Alkyl Oxazoles from N-Propargylamides

Abstract

Here, we report a mild and highly efficient approach to alkyl oxazoles through merging gold/copper catalysis and copper/photoredox catalysis. Various alkyl oxazoles are synthesized from N-propargylamides with alkyl halides in good to excellent yields with wide functional-group compatibility under blue-light irradiation. Significantly, a copper catalyst plays a dual role in this transformation: as a powerful cocatalyst to accelerate protodeauration of vinyl gold intermediates and improve photoredox catalysis.

Synthesis and Antiproliferative Evaluation of d‐Glucuronamide‐Based Nucleosides and (Triazolyl)methyl Amide‐Linked Pseudodisaccharide Nucleosides**

“…[37] The synthesis of dodecyl-containing glucuronamide-based nucleosides comprising a 1,2,3-triazole between the sugar moiety and the purine unit was based on the 1,3-dipolar cycloaddition between 1-azido glucuronamide derivatives and N-propargyl-6-chloropurine (Scheme 4). The glycosyl azides 25, 26 were synthesized in moderate to good yields (46 %, 72 %) via anomeric azidation of N-dodecyl tetra-O-acetylglucuronamide (24), accessible from glucuronolactone 1 as previously reported, [12] and of N-propargyl 1,2,4-tri-O-acetyl-3-O-dodecylglucuronamide (12), respectively, with trimethylsilyl azide. The α-glucuronoamidyl azides 25 α, 26 α, which could be isolated from the respective anomeric mixtures, were then subjected to cycloaddition with N 9 and N 7 -propargyl-6-chloropurines (28, 29), which were obtained in a 3 : 1 ratio (57 % total yield) via nucleophilic substitution with propargyl bromide in the presence of potassium carbonate.…”

“…The formation of the 11 is not surprising since it is well reported that N ‐propargylamides are prompted to cyclize or isomerize into oxazoles under various reaction conditions [23] . Such cyclization has been particularly exploited using metal catalysis [24,25] or iodine‐mediated activation of the triple bond [26–29] . Only a few base‐mediated examples of N ‐propargylamide cyclization into oxazoles have been reported, namely for N ‐(1‐arylpropargyl)amides indicating that allenic intermediates may be involved in such transformation [30–32] .…”

Visible-Light-Promoted Radical Cascade Cyclization of 2-Vinyl Benzimidazoles: Access to Benzo[4,5]imidazo[1,2-b]isoquinolin- 11(6H)-ones

“…Based on the experimental outcomes detailed above and preceding reports on photoredox cascade reactions, , a proposed mechanism for the Ir-catalyzed oxidative quenching cycle is depicted in Figure c. Initially, the photocatalyst, fac -Ir­(ppy) 3 , absorbs blue light and is excited.…”

Fluoroalkyl Iodides in Fluoroalkylative Difunctionalization of C−C Multiple Bonds

“…The latter not only delivers fluoroalkyl radical capable for addition to 37 , but also assist protodeauration in the first step. Shortly after, a more robust protocol merging gold/copper and copper/iridium‐photoredox catalyses was proposed [160] . A dual role of copper co‐catalyst was postulated: acceleration of protodeauration in the cyclization step and facilitates a SET form photocatayst in fluoroalkylation step.…”