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2,3-Dihydro-3-[(S)-1-phenethyl]quinazolinone and some new 2-substituted derivatives bearing isopropyl, o-nitrophenyl and p-nitrophenyl groups were prepared in 40-90% yield by amidation of isatoic anhydride with (S)-phenylethylamine, followed by condensation with triethyl orthoformate, isopropylaldehyde, o-nitro-and p-nitrobenzaldehyde, respectively. The two 2-subtituted dihydroquinazolinones obtained either by using isopropylaldehyde, o-nitro-or p-nitrobenzaldehyde, were separated and purified before their NMR spectra in CDCl 3 solutions were recorded. The detection of the low energy conformation of O=C-N-phenethyl segment in solution allowed the correlation of the NMR data with the configuration of newly stereogenic carbon C-2; thus, one diastereomer was labeled SS while the other was RS. Configurations determined by the NMR method were corroborated by X-ray diffraction analysis. X-ray structures of each diastereomeric series showed characteristic conformational types: a propeller-like for the SS and a hairpin for the RS series. Interatomic distances of the hairpin conformation suggest the existence of intramolecular face-to-face interactions between two aromatic rings. Molecules 2007, 12 174

Photochemical irradiation of 2,3-dihydro-2-tert-butyl-3-benzyl-4(1H)-quinazolinone produced 3-benzyl-4(3H)-quinazolinone through photoinduced elimination via a radical mechanism. The use of photochemical conditions such as chloroform and UV irradiation (λ = 254 nm) got the 3-benzyl-4(3H)-quinazolinone in a high yield. Some theoretical calculations were achieved to explain the mechanism and the presence of radical intermediates was confirmed by trapping with different 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives.4-Quinazolinone derivatives are important building blocks of active molecules isolated from different natural sources. 1 Their principal derivatives are 2,3-dihydro-4(1H)-quinazolinones and 4(3H)-quinazolinones. These compounds possess a wide range of useful biological activities and interesting pharmacological properties, 2 and their syntheses have been well described in the literature. 3 The use of photochemical irradiation in these compounds, however, has been less common, and only a few have been reported such as preparation of fused quinazolin-4-one derivatives, for example, luotonin A and related fused compounds through radical intermediates, 4 photodecomposition of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine (Midazolam) to get a 4(3H)-quinazolinone derivative, 5 and irradiation of 4-phenylquinazolin-2-ones in the presence of a hydrogen donor in order to get the reduced 3,4-dihydroquinazolin-2-ones 6 as well as the photoaddition of 4(3H)-quinazolinone derivatives to olefins. 7 In this study we analyzed the behavior of 2,3-dihydro-2-tert-butyl-3-benzyl-4(1H)-quinazolinone under UV irradiation, and theoretical calculations were developed to propose a mechanism, and trapping of the radical intermediate was achieved using TEMPO derivatives. Knowledge of these reactions could help to develop photochemically controlled reactions of other 2,3-dihydro-4(1H)-quinazolinone derivatives.Our research was focused on the preparation of starting materials following the methodology previously reported by our group 8 in which a reaction between isatoic anhydride and benzylamine in ethyl acetate at 40°C results in the corresponding aminobenzamide 1 in 90% yield. Next, the cyclocondensation of 1 with pivalaldehyde in dichloromethane and p-toluenesulfonic acid monohydrate gives 2 in 86% yield (Scheme 1).Preliminary studies rapidly led to the conclusion that it was necessary to protect the reaction from light source since this would suffer photoinduced elimination and hence reduces the yield of compound 2. The absorption spectrum of 2 ( Figure 1) presents two absorption bands at λ = 242 and 341 nm, attributed to π-π* and n-π* transitions, respectively. The fluorescence spectrum is shown in the Figure 2 and presents a maximum emission at λ = 404 nm. The quantum yield of fluorescence was measured at 25°C using quinine sulfate (H 2 SO 4 0.5 M, Φ = 0.55) as standard and employing existing equations for calculating quantum fluorescence yield;

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