Transition-metal-free radical relay cyclization of vinyl azides with 1,4-dihydropyridines involving a 1,5-hydrogen-atom transfer: access to α-tetralone scaffolds

Abstract

The remote C(sp3)–H functionalization enabled by a radical-mediated 1,5-hydrogen-atom transfer (HAT) process using vinyl azides and 1,4-dihydropyridines as precursors has been described.

Na2S2O8‐Mediated Tandem One‐Pot Construction of 3,3‐Disubsituted 3,4‐Dihydroquinoxalin‐2(1H)‐ones with 4‐Alkyl‐1,4‐dihydropyridines as Alkyl Radical Sources

“…reported a catalyst‐free C−H alkylation of N‐heterocycles and 1,4‐quinones with 4‐alkyl‐1,4‐dihydropyridines at room temperature using inexpensive and stable Na 2 S 2 O 8 as a stoichiometric oxidant [10c] . Similarly, 4‐alkyl‐1,4‐dihydropyridines also participated well in the Mn‐mediated alkylation of β‐chloroketones, [10d] persulfate‐mediated alkylation of alkynes [10e] and 2H‐indazoles [10f] and cyclization of vinyl azides, [10g] Cu(I)‐catalyzed oxidative decarboxylative alkylation of cinnamic acids [10h] and enantioselective alkylamination of unactivated alkenes [10i] . Interestingly, Nakajima et al.…”

Visible-Light-Promoted Multistep Tandem Reaction of Vinyl Azides toward the Formation of 1-Tetralones

“…23−26 Recently, Liu and co-workers reported a transitionmetal-free radical relay cyclization of vinyl azides with 1,4dihydropyridines via a hydrogen-atom transfer process (Scheme 2c). 27 It is worthwhile to develop a method for high-efficiency conversion of alkenyl azides to complex ketones according to its unique nature under mild conditions. Based on the above considerations, it is necessary to develop vinyl azides to react as a useful synthon to participate in construction of high value frameworks.…”

“…Vinyl azides were widely used in the synthesis of polysubstituted aza-aromatic rings including quinolines, phenanthridines, − pyrrole, and pyrroline . As a high atom economical R· radical acceptor and iminyl radicals donor, it has huge potential in tandem reactions. − For instance, vinyl azides could generate iminyl radicals after attack by R·, and further add to adjacent aromatic rings (Scheme a). − However, vinyl azides are unstable under heating or light irradiation and easily produce a 2 H -azirine intermediate to engage in [3 + 2] cycloaddition with alkynes (Scheme b). − Recently, Liu and co-workers reported a transition-metal-free radical relay cyclization of vinyl azides with 1,4-dihydropyridines via a hydrogen-atom transfer process (Scheme c) . It is worthwhile to develop a method for high-efficiency conversion of alkenyl azides to complex ketones according to its unique nature under mild conditions.…”

K2S2O8‐Mediated Oxysulfonylation of Vinyl Azides with Sodium Sulfinates to Access β‐Keto Sulfones in Water

“…Vinyl azides are very significant synthons and are commonly used as a radical acceptor to construct various molecular skeleton, such as β‐sulfonyl enamines, [35] α‐trifluoromethylated ketones, [36] β‐keto sulfones, [25] phenanthridines, [37,38] nitriles, [39] quinolines, [40] pyridines, [41] imidazo[1,2‐ a ]‐pyridine, [42] α‐tetralone [43] and O‐phthalimide oxime [44] . We envisage that the newly formed sulfonyl radicals that generated from sodium sulfinates 2 may attack the C−C double bond of vinyl azide 1 and subsequently the radical addition occurs to furnish the iminyl radical with the release of N 2 on account of the unique chemical properties of the azide group.…”