Scheme 43


hv solid




EtOCO Me Scheme 45

In the solid state different paths are observed, and can be rationalised with reference to the crystal packing. Thus, levonorgestrel160 (146b, R=Et, R-H) as well as ethisterone (146c, R, R-Me) and norethisterone (146a)161 undergo photo-dimerisation in the solid state under nitrogen; compound (155) is formed from (146a) (Scheme 42). Crystalline lynestrenol is also photoreactive, while mestranol and progesterone have shown good photostability.162 Testosterone propionate (156) gives dimer (157) when irradiated in the solid state (Scheme 45).163 Testosterone (158) disporportionates to androstenedione (159) and androstanedione (160) and 17-methyltestosterone (161) give the seco derivative (162) under that condition

Scheme 46

A number of stilbene derivatives are used as synthetic estrogens. The photochemistiy of stilbenes has been investigated in depth. E-Z photo-isomerisation is always a fast process and the Z isomer undergoes conrotatory electrocyclic ring closure to give a trans fused dihydrophenanthrene; in the presence of various oxidants (often atmospheric oxygen is sufficient) this intermediate is then aromatised.165 As expected, clomiphene (163 a, R=C1) isomerises when irradiated in chloroform, and each isomer cyclises to the corresponding phenanthrene, (164) and (165) respectively (Scheme 47).166


Ph o

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