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Extracts of Stereocaulon vesuvianum Pets, showed strong activity against Bacillus subtilis and Escherichia coli and a distinct activity against Penicillium digitatum and Saccharomyces cerevisiae. By preparative hplc, methyl ß-orcinolcarboxylate (strongly antifungal) and atranol (strongly antibacterial) were isolated, and it was shown that both compounds are present as natural products and are not artifacts formed during workup. Methyl ß-orcinolcarboxylate was recently suggested to be present in S. vesuvianum by the revision (1) of an isomeric structure previously reported (2) in this species. Sizable amounts of the common cortical depside atranorin (inactive) were also isolated. EXPERIMENTALPlant material.-S. vesuvianum was collected on the middle slopes (ca. 1300 m) of Mt. Etna. It grows abundantly only on the ancient (2-3 centuries old) lava flows. A voucher specimen is deposited at the University of Catania.

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The photochemical rearrangement of several 3heteroaryl substituted cyclopropenes has been studied. The rearrangements are derived from the '~t--'lt* singlet state of the cyclopropene. Ring opening occurs to give a vinylcarbene intermediate which undergoes a subsequent electrocycliration. The transient intermediate so produced can undergo either a 1,3-or a 1,5-sigmatropic hydrogen shift to give the observed products. One strong piece of evidence for carbene intervention is the observation of a 1,3-butadiene derivative as one of the photoproducts obtained from the photolysis of a 3-pyrrolyl substituted cyclopropene. The 1,3-diene is thought to be derived by insertion of the vinylcarbene into the neighbouring methyl group. The regioselectivity of the rearrangement can be accounted for in terms of competitive 1,3and 1,5-sigrnatropic hydrogen migrations.