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Singlet oxygen is the reactive intermediate in some 9,lO-dicyanoanthracene (DCA) sensitized photooxygenations. The limiting quantum yield of singlet oxygen production approaches 2 in benzene and acetonitrile. Singlet oxygen formation was characterized by its emission at 1270 nm and by its reaction with acceptors. There is an increase in '02 luminescence intensity under oxygen relative to air. The high yield of IO2 and the oxygen concentration dependence are consistent with energy transfer from ' DCA to 302 to give '02 and 3DCA, which subsequently produces a second molecule of IO2. (24) Wegner, E. E.; Adamson, A. W. J. Am. Chem. SOC. 1966,88,394. (25) Ogilby, P. R.; Foote, C. S. J. Am. Chem. SOC. 1982, 104, 2069. (26) The quantum yields of '02 production from DNT, determined in the same manner as the DCA-sensitized singlet oxygen quantum yields in the 2M2P experiments, are 0.98 & 0.03 in C6HB and 0.62 0.07 in CH&N.

1): apparently, 2a is not reactive enough. Formation of the desired isomer 3 dominated over that of 4 by the ratio 4 : 1. The same ratio of isomers was obtained with zinc chl~ride-ether [~"' (No. 2); although this reaction was carried out at -4O"C, some of the product decomposed at longer reaction times. We therefore activated the allylic alcohol by trifluoroacetylation to afford 2b and found that prenylation was feasible in refluxing dichloromethane (No. 3). Interestingly, on lowering the temperature to 25°C prenylation was more regioselective; formation of 3 was preferred still more (3 : 4 = 89 : 11 ; No. 4). The total isolated yield of 3 + 4 was 73%. Products arising from attack of the tertiary allylic terminus on l a were not detected.We found, however, that tertiary alkyl groups can be introduced into furans by a different method, i. e. by reaction with 4-methyl-2-0~0-3-pentenenitrile 5['] in the presence of aluminum chloride in benzene (Scheme 1). This reagent is R 2) MeOH l a : R = Me Ib: R = H R R 6a: R = Me (37%) 7a: R = Me (2.4%) 6b: R = H (43%) + CX30&OCH3 8a: 8b: R R = = H M e (10%) (19%) The photodynamic fungal pigment cercosporin 1['] is a nonspecific toxin which kills plant cells in vitro in the presence of light by lipid p e r o x i d a t i~n [~,~~] .The requirement for light, the cercosporin-sensitized formation of the characteristic '0, oxidation product of cholesterol (the 5a-hydroperoxide), and the inhibition of the effects of cercosporin by /%carotene and other '0, quenchers suggest that the mechanism of action involves production of '02 sensitized by lC9. We now report direct evidence for '0, formation by observation of the characteristic '0,-luminescence at 1270 nm sensitized by cercosporin. This is the first time that a plant photodynamic sensitizer has been shown unequivocally to produce singlet oxygen. The quantum yield of 'Oz formation is large: 0.81 f 0.07 (95% confidence level). Scheme 1. Tertiary alkylation of la, b with 4-methyl-2-0~0-3-pentenenitrile 5 in the presence of AIC13. more regioselective than the prenylation reagent; the ratio 6a : 7a was 94 : 6. Compound 6a, which is of the cis-jasmone type, has an interesting herbal, sweet, floral odor. 6a and 6b have also been reduced to the corresponding alcohols 9a and 9b. R 9a: R = Me 6a,b %H 9b: R = H R=CH>CHOHCH,

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