Photochemistry of estra-5,7-diene-3β,17β-diol 17-acetate and its 9,10-seco isomer, 10-desmethyl analogues of pro- and previtamin D. 1. "Reversible" isomerization reactions

Article abstract of DOI:10.1002/recl.19871061003

In analogy with the photochemistry of 7,8-didehydrocholesterol (provitamin D), irradiation of the 10-desmethyl steroid estra-5,7-diene-3β,17β-diol 17-acetate leads to a photoequilibrated mixture of steroid-5,7-dienes and 9,10-seco-5(10),6,8-trienes.In addition, a thermally unstable bicyclo<2.2.0>hexene derivative is found.From the composition of the quasi-photostationary state, the ratios of the quantum yields of the various interconversions are estimated.Differences with the photochemistry in the 10-methyl series are discussed in relation to conformational differences.