4819 180”). In each case ca. 2% isomerization to the cis isomer of the cyclopropane had occurred. Optical density changes of each SOlution as a result of irradiation were negligible.
Acknowledgment.
Petroleum Research Fund, administered by the American Chemical Society, for support of this research. We are also grateful to Professors Gary Griffin and Stanley Cristol for helpful discussions.
We thank the donors of the
Photosensitized Cycloadditions to 1,3-Dimethyl-6-azauracil and 1,3-Dimethyl-6-azathymine.An Imine Linkage Unusually Reactive toward Pho tocycloaddition John S. Swenton* la and John A. Hyattlb3O Contribution from the Department of Chemistry, The Ohio State Unioersity, Columbus, Ohio 43210. Receioed February 14, 1974 Abstract: The acetone-sensitized cycloaddition of 1,3-dimethyl-6-azathymine (lb) and 1,3-dimethy1-6-azauracil (2b) to olefins has been studied. For 2b high yield cycloadducts were formed with ethylene, tetramethylethylene,
isobutylene, ethyl vinyl ether, vinyl acetate, and isopropenyl acetate. In the case of the oxygen-substituted olefins, were formed with greater than 95 regioselectivity. epimeric 8-substituted 1,2,4-triazabicyclo[4.2.0]octane-3,5-diones Photosensitized cycloaddition studies of l b with tetramethylethylene and vinyl acetate indicate that the photochemical reactivity of l b and 2b is qualitatively similar. These results are discussed with reference to the general low photochemical reactivity of imines in cycloaddition reactions.
T
he photochemical reactivity of excited pyrimidine bases2 and their aza analogs3 has attracted much attention in recent years. In particular 6-azathymine ( l a ) and 6-azauracil (2a) derivatives, which theoretically4 should show photochemical behavior similar to thymine and uracil, have shown photochemical reactivity much to the contrary. Thus, P r u ~ o f f has ~ ~ ,re~ ported that 6-azathymine and its ribonucleoside were essentially resistant to the effects of uv irradiation. In addition, the presence of l a in bacterial DNA and the incorporation of l a in Enterococcus stei increased the resistance of these materials toward uv irradiation. While facile photodimerization of neither l a nor 2a has been observed, photohydration of 2a has been recently reported to afford 5-hydroxy-5,6-dihydro-6-azauracil (3).3f,g This hydration product results from the opposite mode of water addition than that observed in uracil derivatives. The low reactivity of these 6-aza analogs toward photodimerization may be viewed in a much larger context, namely the reluctance of >C=N- systems t o undergo bimolecular 2 2 additions. Thus, while
+
( 1 ) ( a ) Alfred P. Sloan Fellow, 1971-1973, Camille and Henry Dreyf u s Teacher-Scholar, 1972-1977. (b) Ohio State University Fellow, 1971, 1973. (c) For a preliminary report, see J. A. Hyatt and J. S. Swenton, J. Chem. Soc., Chem. Commun., 1145 (1972). ( 2 ) For leading references, see J . S. Swenton, J. A. Hyatt, J. M. Lesy, and J. Clardy, J . Amer. Chem. Soc., 96,4885 (1974). (3) (a) W. Prusoff, Biochim. Biophys. Acta, 58, 588 (1962); (b) H. Gunther and W. Prusoff, ibid., 49, 361 (1967); (c) A. Wacker, H. Dellweg, L. Trager, A. Kornhauser, E. Lodeman, G. Turch, R. Selzer, P. Chandra, and IC=Nlinkage we have investigated the generality of this process. We wish to report here the high yield acetone photosensitized cycloadditions of 1,3-dimethyl-6-aza(5) (a) R. Warrener and J. Brenner, Ret-. Pure A p p l . Chem., 16, 117 (1966); (b) W. Dilling, Chem. Rec., 66, 373 (19661, (c) “Photochemistry,” Vol. 4, D. Bryce Smith, Ed., The Chemical Society, Burlington House, London, 1960. (6) D. Arnold, Adcan. Photochem., 6 , 301 (1968). (7) (a) E. T. I
