6-O-Methylarthothelin (5) (2,4,5-trichloro-1,3-dihydroxy-6-methoxy-8- methyl-9H-xanthen-9-one) and 1,3,6-tri-O-methylarthothelin (7) (2,4,5- trichloro-1,3,6-trimethoxy-8-methyl-9H-xanthen-9-one) have been synthesized and shown to cooccur with norstictic acid, connorstictic acid, atranorin and 2,4,5-trichlorolichexanthone (4) in a Dimelaena lichen.

The e.s.'r. spectra of a variety of silyl radicals have been observed during the steady-state photolysis of di-t-butyl peroxide in the parent silane. In a number of cases, in addition to the proton hyperfine interactions, splittings from 29Si in natural abundance have been observed. Unlike the analogous alkyl radicals, silyl radicals are non-planar around the atom bearing the unpaired electron. In the series (Me),SiH,-, the radicals probably become less planar as Me is replaced by H.

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2,5-Dichloro-6-O-methylnorlichexanthone (8) (2,5-dichloro-1,3-dihydroxy-6-methoxy-8-methyl-9H-xanthen-9-one) and 4,5-dichloro-6-O-methylnorlichexanthone (9)(4,5-dichloro-1,3-dihydroxy-6-methoxy-8-methyl-9H-xanthen-9-one) have been synthesized and shown to co-occur with norstictic acid, connorstictic acid, atranorin, 6-O-methylarthothelin (4), 2,4,5- trichlorolichexanthone (5), 1,3,6-tri-O-methylarthothelin (6) and thiophaninic acid (7) in an Australian Dimelaena lichen.

No abstract