Crystal structure of 4,13-dimethyl-3,7,10,14,19,22,25-heptaoxapentacyclo- [25.0.0(1,6).0(6,26).0(11,16).0(11,18)]heptacosa-4,11-diene-2,15-dione.
of conjugated enones with olefins are useful for making a cyclobutane ring system. We have previously reported on the intermolecular photocycloaddition reactions of 2-pyrones with olefins,1–3 and the intramolecular photodimerization reactions of 4,4′-polymethylenedioxy-di-2-pyrones4 to clarify the reactivity involving the study of peri-, site, and stereoselectivities. As a part of an application of the cycloaddition reactions, we have planned to synthesize a macrocyclic compound possessing two cyclobutane rings using double photocycloaddition reactions of 6,6′-dimethyl-4,4′-dimethylenediox-di-2-pyrone (1) with di(ethylene glycol) divinyl ether (2). A solution of (1) (1.39 g), (2) (1.58 g), and xanthone (0.98 g) as a sensitizer in acetonitrile (500 ml) was irradiated with a 400W high-pressure mercury lamp (>350 nm ) for 20 h under a nitrogen atmosphere. After removing the solvent, an oily residue was chromatographed by silica gel (eluent: ethyl acetate–hexane) to give a solid product (3) in 20% yield, which was recrystallized from ethyl acetate. Since the usual analytical and spectroscopic techniques do not permit the identification of two types of isomers, (3) and (4) (in Fig. 1), an X-ray diffraction study of the product was carried out to determine the structure. Data collections were performed at 93 K with graphitemonochromated Mo Kα radiation on a Rigaku RAXIS-RAPID Imaging Plate diffractometer (λ = 0.71069 Å). Lorentz and polarization corrections were applied to the intensity data. The structure was solved by direct methods using SIR 92.5 The structure was refined by a full-matrix least-squares method. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined isotropically. All calculations were performed using the teXsan6 crystallographic software package. Table 1 gives the crystal data and experimental conditions. Figure 2 is an ORTEP diagram of the molecule, which shows the atomic-labeling scheme. The final positional parameters are given in Table 2, and selected bond lengths and angles are listed in Table 3. 1017 ANALYTICAL SCIENCES AUGUST 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry
Site-selective photocycloadditions of 2-pyrones with electron-poor olefins and the derivation from the cycloadducts
Photosensitized cycloaddition of 4,6-dimethyl-2-pyrone (1) with methacrylonitrile (3b) afforded two types of [2+2]cycloadducts, oxabicyclo[4.2.0]octenes 4b and 6b, across the C 5 -C 6 and C 3 -C 4 double bonds in 1, respectively. Photosensitized reactions of 1 with dimethyl maleate and dimethyl cyclobutene-1,2-dicarboxylate gave [2+2]cycloadducts oxabicyclo[4.2.0]octenes 4d, oxatricyclo[4.4.0.0 7 ,10]decene 4e across the C 5 -C 6 double bond, in addition to [2+2]cycloadduct oxabicyclo[2.2.2]octene 9d or bicyclo[4.2.0]octadiene 10e. The photoreactions of methyl 2-pyrone-5-carboxylate (2) with 3b and 2-chloroacrylonitrile (3c) gave [2+2]cycloadducts oxabicyclo[2.2.2]octene 5b, 5c in addition to [2+2]cycloadducts oxabicyclo[4.2.0]octenes 11b and 11c across the C 5 -C 6 double bond in 2. The ptotocycloaddition mechanism was explained from results calculated by means of PM3-CI method. Namely, the site- and:or regio-selectivite products, 4,5,8,9 and 10 were thought to come from the same site-selective radical intermediates in the case of electron-poor olefins.
Singlet and triplet photocycloaddition reactions of 2‐pyridones with propenoate and 2,4‐pentadienotes, and the frontier molecular orbital analysis
Regioselective photocycloadditions of 2-pyridones (1) with 2,4-pentadienoates (3) were analysed and compared with the reactions with propenoate (2), and origins of the different regioselectivities were inferred from frontier molecular orbital properties by the use of PM3-CI method. 
 
 
 
Direct photoreactions of 1 with 3 being α,β,γ,δ-unsaturated carboxylates gave four types of regio-selective [2+2]cycloadducts, 3-β:4-α-4, 5, 3-δ:4-γ-6,7,5-δ: 6-γ-8, 9 and 5-δ:6-γ-[2+2]cycloadducts 10,11. Sensitized photoreactions of 1 with 3 did not occur, and fluorescence of 1 was weakly quenched by 3. Otherwise, main cycloadducts in the sensitized reactions of 1 with 2 have been obtained as 5-α:6-β-[2+2]cycloadducts, which were different from main 3-β:4-α-[2+2]cycloadducts of the direct reactions, and these site-and regio-selectivities were inferred from the different frontier molecular orbital coefficients at the. 3-and 6-positions of 1 for the triplet and singlet states. Formations of 4–7 were also interpreted by both effects of frontier orbital HSOMO-LUMO interactions and of the electrostatic interaction between 1 and 3. The other site-and regioselective adducts 8–11 were inferred to be formed by the electrostatic interactions similar to 2-pyridone photodimerization.