Details

Autor(en) / Beteiligte

• Sierra, Sonia
• Dalmau, David
• Alegre-Requena, Juan V
• Pop, Alexandra
• Silvestru, Cristian
• Marín, Maria Luisa
• Boscá, Francisco
• Urriolabeitia, Esteban P

Titel

Synthesis of Bis-oxazolones

Ist Teil von

• International journal of molecular sciences, 2023-04, Vol.24 (8)

Ort / Verlag

MDPI AG

Erscheinungsjahr

2023

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• The irradiation of 2-aryl-4-(E-3′-aryl-allylidene)-5(4H)-oxazolones 1 with blue light (456 nm) in the presence of [Ru(bpy)[sub.3]](BF[sub.4])[sub.2] (bpy = 2,2′-bipyridine, 5% mol) gives the unstable cyclobutane-bis(oxazolones) 2 by [2+2]-photocycloaddition of two oxazolones 1. Each oxazolone contributes to the formation of 2 with a different C=C bond, one of them reacting through the exocyclic C=C bond, while the other does so through the styryl group. Treatment of unstable cyclobutanes 2 with NaOMe/MeOH produces the oxazolone ring opening reaction, affording stable styryl-cyclobutane bis(amino acids) 3. The reaction starts with formation of the T[sub.1] excited state of the photosensitizer [sup.3][Ru*(bpy)[sub.3]][sup.2+], which reacts with S[sub.0] of oxazolones 1 through energy transfer to give the oxazolone T[sub.1] state [sup.3](oxa*)-1, which is the reactive species and was characterized by transient absorption spectroscopy. Measurement of the half-life of [sup.3](oxa*)-1 for 1a, 1b and 1d shows large values for 1a and 1b (10-12 μs), while that of 1d is shorter (726 ns). Density functional theory (DFT) modeling displays strong structural differences in the T[sub.1] states of the three oxazolones. Moreover, study of the spin density of T[sub.1] state [sup.3](oxa*)-1 provides clues to understanding the different reactivity of 4-allylidene-oxazolones described here with respect to the previously reported 4-arylidene-oxazolones.