Photochemische Reaktionen. 68. Mitteilung. Die Photoisomerisierung von α,β-ungesättigten γ,δ-Epoxyketonen: 9α, 10α- und 9β, 10β-Oxido-3-oxo-17β-acetoxy-Δ4-östren

Irradiation in the n→π* absorption band of the α,β-unsaturated γ,δ-epoxyketone 5 in ethanol at ?65° exclusively afforded the rearranged ene-dione 13 , whereas at + 24° under otherwise unchanged reaction conditions or upon triplet sensitization with Michler's ketone and with acetophenone at + 24° essentially identical mixtures of 13 (major product), 14 , and 15 were obtained. Selective π→π* excitation of 5 at ?78° and + 24° led to similar product patterns. The 9β,10β-epimeric epoxyketone 7 selectively isomerized to 14 and 15 at + 24° and n → π* or π → π* excitation. Neither the epoxyketones 5 and 7 nor the photoproducts 13–15 were photochemically interconverted. In separate photolyses each of the latter gave the double bond isomers 16 , 18 , and 19 , respectively. Cleavage of 13 to the dienone aldehyde 17 competed with the double bond shift ( → 16 ) when photolyzed in alcoholic solvents instead of benzene. The selective transformations 5 → 13 (at ?65° and n → π* excitation) and 7 → 14 + 15 are attributed to stereoelectronic factors facilitating the skeletal rearrangements of the diradicals 53 and 55 , the likely primary photoproducts resulting from epoxide cleavage in the triplet-excited compounds 5 and 7 , via the transition states 54 , 56 , and 57 . The loss of selectivity in product formation from 5 at higher temperature and n → π* excitation or triplet sensitization is explicable in terms of radical dissociation into 58 and 59 increasingly participating at the secondary thermal transformations of 53 . The similar effect of π → π* excitation even at ?78° indicates that some of the π,π* singlet energy may become available as thermal activation energy. It is further suggested that the considerably lesser ring strain in 14 and 15 , as compared with 13 , is responsible that selectivity in product formation from 7 is maintained also at +24° and at π → π* excitation.     

Photochemische Reaktionen. 34. Mitteilung. Die Photoisomerisierung von 3-Oxo-Δ1;4-Steroiden in Dioxanlösung. 3,11-Dioxo-17β-acetoxy-Δ1;4-androstadien und 3-Oxo-17β-acetoxy-Δ1;4;9,11-androstatrien

Ultraviolet irradiation of the steroidal cross-conjugated dienones 3 and 7 , and of the bicyclohexenone derivative 16 in dioxane solution produced the virtually quantitative isomerizations 3 → 11 (Chart 3) and 7 → 16 → 17 (Chart 6). These conversions are consistent with the previously established general scheme a → b → c → d → e (Chart 1). By analogy with these results, it is suggested that the photo-isomers 9 and 10 of O-acetylprednisone ( 8 ) represent products resulting from multiple photorearrangements rather than from direct transformations, as had been proposed in the literature.     

The Structure of Cadinane-4α, 9α-Diol-2-Ene

The structure of cadinane-4α, 9α-diol-2-ene, a crystalline compound from acetone extractive of Taiwania cryptomedioides Hayata, was established by chemical behavior and spectrospcopic data.