No abstract

The photochemistry of di-rert-butylselenoketone 1 and selenofenchone 2 has been examined. Their photochemical properties resemble those of thioketones rather than ketones in that hydrogen abstraction occurs from an upper excited state and not from the lowest (n+ n") excited state. Di-terr-butylselenoketone. 1, on irradiation into the S, band forms the diselenide 3. The quantum yield for this process u a s found to be 0.0055 and was increased in the presence of a good hydrogen atom donor. No reaction was observed follo\ving excitation into the S , state unless a good hydrogen atom donor was present. and even then the photoreaction was very inefficient. Quenching experiments with biacetyl demonstrated the lifetime of the abstracting state to be in the order of 1 0 " s. The formation of the diselenide 3 has been rationalized in terms of hydrogen abstraction from solvent by photoexcited 1 and trapping of the radicals produced by ground state 1, leading to the radical 6. The mechanism is supported by esr evidence for the existence of 6. Selenofenchone. 2. also. did not react follo~ving excitation into the S , state, but underwent intramolecular cyclization in a similar manner to bicyclic thioketones following excitation into the S , state.On a examine la stireochimie de la di-tert-butylselenocetone 1 et de la selenofenchone 2. Leurs proprietes photochimiques sont semblables a celles des thiocetones plut8t qu'a celles des cetones ou il se produit une Climination d'hydrogene apartir de l'etat excite superieur et non a partir de l'etat excite le plus faible (n -, n*). L'irradiation de la di-tert-butylselenocetone 1 dans la bande S 2 conduit au diselenure 3. On a trouve que le rendement quantique de cette reaction est de 0:0055 et qu'il augmente en presence d'un bon donneur d'hydrogene. L'irradiation dans la bande S , ne donne pas de reaction a moins qu'un donneur d'hydrogene soit present et. mime dans ces conditions, la rCaction photochimique n'est pas efficace. L'intemuption brusque des reactions a I'aide du biacetyle a montre que la duree de vie de l'etat ou i! y a elimination d'hydrogene est de I'ordre de 1 0 " s. On arationalise la formation du diselenure 3 en fonction d'une Climination d'hydrogene a partirdu solvant par le compose 1 photoexcite et en fonction du piegeage des radicaux produits dans I'ttat fondamental, conduisant au radical 6. Les preuves de I'existence du derive 6 apportees par la rpe confirment le mecanisme propose. L a se1Cnofenchone 2 ne reagit pas nonplus a la suite d'une excitation dans l'etat S , mais il subit une cyclisation intramoleculaire de facon similaire aux thiocetones bicycliques apres une excitation dans l'etat S2.[Traduit par le journal] Pntroductisn Recently Barton and colleagues (1) reported the preparation of the first isolable selenoketones, namely di-ter-t-butylselenoketone, 1, and selenofenchone 2. As is the case with the related thioketones (9, selenoketones possess a low energy electronic transition giving rise to a weak intensity band. S, (T,), in the visible region of the ...

Die Reduktion zahlreicher Oxo‐Verbindungen (I) mit Tributylzinnhydrid (II) zu den Carbinolen (III) wird untersucht und in Tabellen aufgeführt.