Decatungstate-Catalyzed Photochemical Synthesis of Enaminones from Vinyl Azides and Aldehydes

Abstract

Visible light-induced synthesis of enaminones from vinyl azides and aldehydes under decatungstate photocatalysis was developed. The reaction proceeds via acyl radical generation from aldehyde, followed by its addition to vinyl azide, nitrogen elimination, hydrogen atom abstraction by the intermediate iminyl radical, and tautomerization. Photochemical synthesis was efficiently conducted under both batch and flow conditions. The method can be applied to various vinyl azides and aldehydes and provides the desired products in 15−72% yields.

5-(Benzoyloxymethyl)isoxazole-3-carboxylic Acid Ethyl Ester

“…Furthermore, Mitani et al [11] reported that they isolated E-enaminone as an oil, while 5 was a solid with a melting point of 38.5-39.5 °C. On the contrary, the 1 H and 13 C NMR spectra of 5 and the corresponding Z methyl ester reported by Terent ev et al [12] were identical except for the carbinol signals (Table 1).…”

“…In particular, the resonance of the methyl carbon in 5 was shifted downfield by 7.5 ppm (30.3 vs. 22.8 ppm of 5 compared to E-enaminone), and the alkene carbons resonated at 96.8 and 145.5 ppm for Z-enaminone 5 and at 94.2 and >160 ppm for E-enaminone. Furthermore, Mitani et al [11] reported that they isolated E-enaminone as an oil, while 5 was a solid with a melting point of 38.5-39.5 • C. On the contrary, the 1 H and 13 C NMR spectra of 5 and the corresponding Z methyl ester reported by Terent'ev et al [12] were identical except for the carbinol signals (Table 1). The configurations of E-and Z-enaminones are commonly assigned considering that a strong hydrogen bond between N-H and the carbonyl occurs in Z diastereomers, causing the 1 H-N shift to move to a higher frequency [10].…”

Decatungstate‐Catalyzed Carbon‐Carbon Bond Formation Between Furfural and Electron‐Deficient Olefins

“…In the previous investigations on TBADT‐catalyzed additions of benzaldehydes to olefins, the acceptor has been acrylate derivatives, [10b–e,12] 2‐vinylpyridine, [10h] styrene, [10g] phenyl vinyl sulfone, [10j] and acrylonitrile [10a] . The present substrate scope shows that furfural can be added to the same substrates and a number of additional compounds.…”

Tetrabutylammonium decatungstate (TBADT), a compelling and trailblazing catalyst for visible-light-induced organic photocatalysis

“…Terent'ev and coworkers reported a photocatalytic addition reaction of aldehydes and vinyl azides to give the enaminones, using visible light-induced decatungstate photocatalysis with a 36 W LED lamp (395–400 nm), Scheme 54. 79 This approach enables the effective synthesis of enaminones in both batch and flow conditions. The reaction proceeds through the generation of acyl radicals from aldehyde, which were formed via a hydrogen atom transfer of aldehyde by the photoexcited decatungstate anion (W 10 O 32 4− *).…”