No abstract

tion of 2,3-dimethyl-2-butene further confirmed its identity as lo2.After correction for differing sensitizer optical densities, the maximum intensities of 1and 2-sensitized '02 luminescence were compared. Since the quantum yield of triplet formation from 2 is 0.81[51, and this state is efficiently quenched by oxygen to form 'Oz[51, the absolute quantum yield of cercosporin-sensitized formation of 'Oz could be determined. Based on four independent determinations, the relative ratio of luminescence produced from 2 to that produced from 1 was found to be 1.01f0.04. Two separate determinations of the relative rates of photooxygenation of 2-methyl-2-pentene in benzene sensitized by 2 and 1 gave the ratio 1.00-+0.12. Both ratios indicate that the quantum yield of formation of '02 sensitized by 1 is 0.81 f 0.07.This large quantum yield strongly supports the suggestion that singlet oxygen is the toxic agent in host plants. This is a striking example of the use of a chemical mechanism by a parasite to gain an "environmental advantage". . Chem. Soc. Farad. Trans. I 76 (1980) 852.[6] Cercosporin was provided by Dr. M. E. Daub, Michigan State University.Its structure and purity were confirmed by comparison of the absorption and NMR spectra with published data"'. 2-Methyl-2-pentene (Aldrich) was purified by column chromatography on basic A1203. C6H6 (Mallinckrodt) was distilled from P20, immediately before use. 2 (Sigma) and C6H6 (Cambridge Isotope Laboratories) were used as received.-The apparatus used to observe '02 luminescence has been described previously 141.Dedicated to Professor Giinther 0. Schenck on the occasion of his 70th birthdayWe recently presented a widely applicable concept for the synthesis of cyclopentanoid natural products based on the utilization of tricyclo[3.3.0.02~8]octan-3-one 1 as central optically active building block"*21. Scheme 1 outlines the strategy (AB + C principle) now chosen by us for the preparation of the tetracycloundecanes 9 and 12, which are potential precursors for the synthesis of coriolins"'. The most important step in the sequence involves the previously only indirectly dernon~trated~~' anti-annelation of a third five-membered ring to 1. tion of the rings A and C in 13 could be confirmed by an X-ray structure analysis. ie H U 9 lh -0 L 10

Dedlcated to Professor Gunther

SummaryThe UV. irradiation of 17B-hydroxy-4a, 5 a -epoxy-2-azaandrostan-3-one (1) yields 17@-hydroxy-2-aza-l0 (5 + 4-abeo)-45 (H)-androsta-3,5-dione (3).Introduction. -We have reported that steroidal lactones behave photochemically in a similar way to their carbocyclic counterparts: a,B-unsaturated lactones, for example, undergo the 'type A' [2] and the di-z-methane [3] rearrangements, while a,@-epoxylactones suffer the 10 (5 4 4 ) rearrangement to an abeo structure [l]. Therefore, as a part of a systematic study on the photochemical behaviour of heterocyclic steroids, we investigated the UV. irradiation of the a , B-epoxylactam 1 (Scheme).

Das vollständige Manuskript dieser Zuschrift erscheint in: Angew. Chem. Suppl. 1983, 1053. DOI: