In the 1,5-1actone compound, C6H804, the lactone ring adopts a conformation between sofa and half-chair. The five-membered ring in the 1,4-1actone, C6H804, is planar and the side chain is in a staggered conformation. The crystal structure of the 1,5-1actone is stabilized by both O---H...O and C--H...O hydrogen bonds and that of the 1,4-1actone by O---H-..O hydrogen bonds. (Johnson, 1965) plot and the numbering scheme of the 6-1actone. The bond lengths and angles observed in this structure are comparable with those of other related naturally occurring lactones, such as asperlin, aspedinol (Fukuyama, Katsube, Noda, Hamasaki & Hatsuda, 1978) and goniotriol (Alkofahi, Ma, McKenzie, Byrn & McLaughlin, 1989). In general, the observed bond lengths are shorter than the normal values, e.g. the C1---C2 single-bond distance of 1.469 (3)/~ is much less than the usual value and may be attributed to the effect of the neighbouring C==O and C==C bonds. The 6-1actone ring adopts a conformation in between sofa and half-chair, the corresponding asymmetry parameters are ACs(C2) = 0.099 (1) and AC2(C1--C2) = 0.045(1) (Nardelli, 1983a), with more tendency towards half-chair conformation. This intermediate conformation of the lactone ring is observed in asperlin and in the chloro-derivative of asperlinol, but the sofa conformation is favoured in asperlinol and goniotriol. The two hydroxyl groups A displacement ellipsoid plot with the numbering scheme of the 7-1actone is given in Fig. 2. The molecule consists of a five-membered ring system comprising the lactone group and an acyclic side chain. The bond lengths and angles are generally comparable to those values expected for the type of hybridization and also with those observed in related structures, such as L-ascorbic acid (Hvoslef, 1968), 2-acetamido-2,3-dideoxy-D-erythro-hex-2-enono-l ,4-1actone (RuzicToros & Lazarini, 1978, D-iso-ascorbic acid (Azamia, Berman & Rosenstein, 1972). The C----C bond lengths are in the range 1.448 (4) ExperimentalThe crystals of the two title compounds were obtained from ethyl acetate solution. Compound (2b)Crystal data 168.5 (2) Symmetry codes: (i) -x, y-½, 1 -z; (ii) 1 +x, y, z; (iii) -x, y -½, -z; (iv) -x, ½ + y,-z; (v) x, y, 1 + z. Compound (3)Crystal data (,4,, o)for (3) Ol---C1 1.361 (3) c 1----c2 01----c41.448 (3) c2--c3 O2--c 1 1.212 (3) c3--c4 03----c51.423 (3) c4---C5 04----c61.415 (3) c5---c6 AbstractThe title compound, 3-phenyl-l,3(4H)-benzoselenazine-2,4(3H)-dione, C14H9NO2Se, was found to crystallize in space group P212121. The ten atoms in the benzoselenazine ring system are planar to within 0.040 (3)A,, with both carbonyl O atoms being slightly out of this plane. The dihedral angle between the phenyl ring and benzoselenazine system is 87.41 (8) °. CommentWork in our laboratories has been directed towards the design and understanding of synthetic methods involving free-radical homolytic substitution at selenium. Recently, we began to explore the use of pyridine-2-thionoxycarbonyl (PTOC) carbamates as precursors to ...

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