Photochemical reactions VII [1]. A ‘type A rearrangement’ in the photolysis of a steroidal α, β‐unsaturated lactone

Abstract

SummaryThe irradiation of 17~-hydroxy-2-oxa-androst-4-en-3-one (1) yields a cyclopropane derivative 2, which is the result of a rearrangement, formally analogous to the 'type A rearrangement' of the enones. Two other products, the dihydroxy compound 5 and the dimer 6, have also been isolated (Scheme I).The photochemical behaviour of the unsaturated lactones has been less widely studied than that of the corresponding ketones. Usually, these lactones dimerise by a well known and documented process [2]. More recently, other reactions like deconjugation [3] or a-fragmentation to ketenes [4] have been described. The three reaction types are formally analogous to the situation described in the case of ketones. Nevertheless, to our knowledge, the rearrangement, well known in the case of cyclic enones [5] ('type A rearrangement', i.e. 3 + 4 [6]) has not been observed in the lactone series.To study this possible photorearrangement of a lactone, compound 1 [7] was selected as model compound.UV.-irradiation of 1 in t-butyl alcohol, in identical conditions as used in the case of testosterone, yields a mixture of the cyclopropane derivative 22) (10,3%), starting material 1 (36,1%), a dihydroxy compound 53) (3,2%) and dimeric material The structural relationship between 2 and 4 has been demonstrated by an independent synthesis of 2. As starting material the cyclopropane derivative 8, obtained 63) (27,2%).

ChemInform Abstract: PHOTOCHEMICAL REACTIONS. XIV. A NORRISH TYPE I CLEAVAGE IN THE PHOTOLYSIS OF A STEROIDAL α,β‐UNSATURATED Δ‐LACTONE

“…In the monocyclic series, Matsuo et al have reported addition of the solvent in the irradiation of 5,6-dihydro-6-methyl-2Hpyran-2-one [3]. Recently, we have been able to show that the 2-oxa-d4 and 4-oxasteroidal lactones undergo, respectively, the type A [4] and di-z-methane [5] photorearrangements in a similar way to their carbocyclic counterparts. In this paper we describe the results obtained in the irradiation of the A'-lactone 1.…”

Photochemical Rearrangement of a Steroidal α, β‐Epoxylactam. Photochemical reactions, XII [1]

“…irradiation of 17B-hydroxy-4a, 5 a -epoxy-2-azaandrostan-3-one (1) yields 17@-hydroxy-2-aza-l0 (5 + 4-abeo)-45 (H)-androsta-3,5-dione (3).Introduction. -We have reported that steroidal lactones behave photochemically in a similar way to their carbocyclic counterparts: a,B-unsaturated lactones, for example, undergo the 'type A' [2] and the di-z-methane [3] rearrangements, while a,@-epoxylactones suffer the 10 (5 4 4 ) rearrangement to an abeo structure [l]. Therefore, as a part of a systematic study on the photochemical behaviour of heterocyclic steroids, we investigated the UV.…”