PHOTOCHEMICAL REACTIONS .52. PHOTOCHEMISTRY OF ALPHA BETA-UNSATURATED CYCLIC KETONES . SPECIFIC REACTIONS OF N,PI'- AND PI,PI'-TRIPLET STATES OF O-ACETYLTESTOSTERONE AND 10-METHYL-DELTA-1,9-OCTALONE-2

The photochemistry of the conjugated cyclohexenones O‐acetyl testosterone (1) and 10‐methyl‐Δ1,9‐octalone‐(2) (24) has been investigated in detail. The choice of reaction paths of both ketones depends strongly on the solvent used. In t‐butanol, a photostationary equilibrium 1 ⇄ 3 is reached which is depleted solely by the parallel rearrangement 1 → 5 (Chart 1; for earlier results on these reactions see [2a] [6] [7]). In benzene, double bond shift 1 → 16 (Chart 3) occurs instead, which is due to hydrogen abstraction from a ground‐state ketone by the oxygen of an excited ketone as the primary photochemical process. In toluene, the major reaction is solvent incorporation (1 → 17, Chart 4) through hydrogen addition to the β‐carbon of the enone, accompanied by double bond shift and formation of saturated dihydroketone as the minor reactions. Contrary in part to an earlier report [19], the photochemical transformation of the bicyclic enoné 24 exhibit a similar solvent dependence. The corresponding products 25–29 are summarized in Chart 5 and Table 1. Sensitization and quenching experiments established the triplet nature of the above reactions of 1 and 24. Based on STERN‐VOLMER analyses of the quenching data (cf. Figures 2, 4–8, and Table 3), rearrangement, double bond reduction and toluene addition are attributed to one triplet state of the enones which is assigned tentatively as 3(π, π*) state, and the double bond shift is attributed to another triplet assigned as 3(n, π*) state (cf. Figure 9). The stereospecific rearrangement of the 1α‐deuterated ketone 2 to the 4β‐deuterio isomer 4 shows the reaction to proceed with retention at C‐1 and inversion at C‐10. The 4‐substituted testosterone derivatives 33–36 (Chart 8) were found to be much less reactive in general than 1. In particular, 4‐methyl ketone 33 remains essentially unchanged on irradiation in t‐butanol, benzene and toluene. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim