[18]Annulene 1,4:7,10:13,16-trisulphide has been synthesized. It has been found to be a stable non-planar non-aromatic system in which the three thiophen rings are linked by three essentially olefinic vinylene groups.

Two new diphenyl ethers, 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxybenzoic acid (micareic acid) (13), 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxy-3-methoxybenzoic acid (methoxymicareic acid) (27) and a new depside, 4-(2-heptyl-6-hydroxy-4-methoxybenzoyloxy)- 2-heptyl-6-hydroxybenzoic acid (prasinic acid) (34) have been detected in chemical races of the lichen Micarea prasina Fr. and isolated and characterized as the corresponding methyl esters. The structure of the latter compounds has been confirmed by total synthesis. The key steps in the synthesis of the diphenyl ethers (14), (26) involved Ullmann-like condensation between the 3-chloro 2-enone (17) and the phenols (11), (31), and subsequent aromatization of the enol ethers (23) and (32). A biomimetic-type synthesis of methyl micareate (48) has also been achieved by treatment of the depside (33) with sodium hydride in dimethylformamide.

The Australian, New Zealand and Papua New Guinean representatives of Hypogymia are reviewed. Photographs, keys and descriptions are given for the 11 species and five varieties. Two new species are described, H. enteromorphoides and H. kosciuskoensis, as well as a new variety, H. subphysodes var. austerodioides and six new combinations are made, namely H. lugubris var. sublugubris, H. lugubris var. compactior, H. pulchrilobata, H. pul- verata, H. tubularis and H. turgidula. Distribution of these taxa is discussed and maps have been provided. The species included in this revision are H. billardieri, H. enteromorphoides, H. kosciuskoensis, H. lugubris, H. mundata, H. pulchrilobata, H. pulverata, H. subphysodes, H. tubularis, H. turgidula and H. vittata.

The depsidones divaronic acid (24) (8-hydroxy-3-methoxy-1,6-dipropyl-11- oxo -11H- dibenzo [ b,e ][1,4]dioxepin-7-carboxylic acid) and stenosporonic acid (25) (8-hydroxy-3-methoxy-6-pentyl-l-propyl-ll-oxo-l1H-dibenzo[ b,e ][1,4]dioxepin-7-carboxylic acid) have been prepared by unambiguous synthesis, and have been shown to cooccur with colensoic acid, atranorin and chloroatranorin in the lichen Paraparmelia mongaensis. The syntheses employed a novel biomimetic-type approach which involved a Smiles rearrangement of a precursor meta-depside in the key step. This rearrangement has important biosynthetic implications and may account for the natural occurrence of isostructural depside-depsidone pairs.

The structure of the lichen diketopiperazine, picroroccellin, has been studied by the synthesis of several of its degradation products.The three possible formulations of methylanhydropicroroccellin (3), (4) and (5) were synthesized and from the physical and chemical properties, the former two compounds were shown to be dissimilar from the naturally derived material. Furthermore, the reactivity of the 3-methoxypiperazine-2,5-dione (5) entirely paralleled that reported for picroroccellin and was consistent with the oxygen functions being located at the 3-and 6-positions of the piperazine-2,5-dione ring. Dimethylpicroroccellin (23) was synthesized, so establishing the trans-stereochemistry of this compound. The properties of (23) were identical with those recorded for the naturally derived material. Hence we conclude that picroroccellin should be reformulated as (2).