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
Intramolecular photocycloadditions of 6,6′‐dimethyl‐4,4′‐polymethylenedioxy‐di‐2‐pyrones
Photosensitized reactions of 4,4′-polymethylene-di-2-pyrones 2b-e afforded [2+2]-cycloadducts 3-5, site-selectively. The selectivity depended upon the methylene chain length. Namely, the three carbon chain gave a syn head-to-head adduct 3b at the 3,4-position of the 2-pyrone ring, the four to six carbon chains gave syn head-to-head adducts 4c-e at the 5,6-position and/or anti head-to-head adducts 5d,e at the 5,6-position, respectively. The intramolecular cycloaddition mechanism was also explained from results calculated by means of PM3-CI method.
Photoadducts of 4,6-Dimethyl- and 4-Methoxy-6-methyl-2-pyrones with Chloroethylenes and Their Dehydrochlorination
Sensitized photoreactions of 2-pyrones with chloroethylenes gave two kinds of [2+2]cycloadducts, 2-oxabicyclo[4.2.0]oct-4-en-3-ones (4, 8) and across the C3–C4 double bond in 2-pyrone, benzene derivatives, and/or cyclobutanecarboxylic acids: Their relative yields greatly depended upon the nature of the reactants. The dehydrochlorination of the cycloadducts 4 and 8 across the C5–C6 double bonds in the pyrones with triethylamine in ethanol gave 5-ethenyl-2-pyrones, whose structures were previously incorrectly assigned as oxocinones, via a symmetry-allowed ring opening of 2-oxabicyclo[4.2.0]octa-4,6-dien-3-ones. Some 5-ethenyl-2-pyrones possessing a chlorinated ethenyl group finally affords 5-ethynyl-2-pyrones by an anti-elimination of hydrogen chloride. The X-ray crystallographic analyses of 5-ethenyl- and 5-ethynyl-2-pyrones are also described.