Cross-Dehydrogenating Coupling of Aldehydes with Amines/R-OTBS Ethers by Visible-Light Photoredox Catalysis: Synthesis of Amides, Esters, and Ureas

Abstract

A straightforward synthesis of amides, ureas, and esters is reported by visible-light cross-dehydrogenating coupling (CDC) of aldehydes (or amine carbaldehydes) and amines/R-OTBS ethers by photoredox catalysis. The reaction is found to be general and high yielding. A plausible mechanistic pathway has been proposed for these transformations and is supported by appropriate controlled experiments.

Metal‐Free Oxidative Amidation of Aromatic Aldehydes using an Anthraquinone‐Based Organophotocatalyst

“…Notably, 5 was produced by the reaction of BHT with singlet oxygen generated by the anthraquinone photocatalyst under visible light irradiation conditions (Scheme ). The results of this experiment indicated that the reaction was not mediated by the photocatalytically generated singlet oxygen, as previously reported in the literature . As already mentioned, anthraquinone is known and used as a catalyst for the production of hydrogen peroxide .…”

Organophotoredox‐Mediated Amide Synthesis by Coupling Alcohol and Amine through Aerobic Oxidation of Alcohol

“…Interestingly, amide formation was also observed without the addition of DIPEA (Table , entry 7). This reaction occurred because piperidine can donate a single electron to PC and thereby forms a piperidine radical, which may attack the carbonyl bond of the aldehyde and subsequent proton abstraction by O 2 .− produced the amide . Air in place of O 2 provided a diminished yield (Table , entry 8).…”

“…This reactiono ccurred because piperidine can donate as ingle electron to PC and therebyf orms ap iperidine radical, which may attack the carbonyl bond of the aldehyde and subsequent proton abstraction by O 2 C À produced the amide. [25] Air in place of O 2 providedadiminished yield (Table 1, entry 8). The use of eosin Y, rose bengal,a nd [Ru(bpy) 3 ] 2 + (bpy = 2,2'-bipyridine) as aP Cf ailed to produce amide 1 (Table 1, entries 9-11).…”

“…Scheme2.Substratesscope of the photocatalytic amidesynthesis from alcohols and amines. Reactionconditions: alcohol (1 equiv, 0.4 mmol), PC (2 mol %), quinuclidine (30 mol %), TBAP (50 mol %), 3 molecular sieves were added to solvent (5 mL) and exposed to a2 3WCFL lampf or 5-10 hi n presence of O 2 and then amine (1.2 equiv)a nd DIPEA( 2equiv) were added and the reaction mixture was irradiated for another 15-20 h. benzyla nd allyl amines were accessed easily to form amide bonds (Scheme 2, compounds [22][23][24][25]. 1-Naphthylamineg enerated the corresponding amide with moderate yield (Scheme 2, compound 26).…”

Photochemical benzylic bromination in continuous flow using BrCCl3 and its application to telescoped p-methoxybenzyl protection

“…29 It has seen numerous applications in atom-transfer radical addition (ATRA) reactions, both photochemically 30,31 or by classical radical methods [32][33][34][35] and also as an oxidizing agent; used directly, [36][37][38] or within a photoredox catalytic cycle. [39][40][41][42] It was anticipated that by utilizing advancements in light source and reactor technology, an improved methodology could be developed. Accordingly, the advantages of simple separation of a single by-product (CHCl 3 ), highly concentrated reactions without precipitation of solid reagents and the possibility of accessing electron-rich benzyl bromides may be realized (Scheme 1).…”