The “overirradiation products” of previtamin D and tachysterol: Toxisterols

The structures of the “toxisterols”, products formed upon prolonged irradiation of previtamin D and its photoisomers, have been investigated. Irradiations (λ > 300 nm) were carried out both in diethyl ether and in alcoholic solvents under conditions where the thermal isomerization to vitamin D is suppressed. From the irradiation mixtures a total of thirteen toxisterols have been isolated. On the basis of structural similarities they have been classified into six categories. In ethereal solution two bicyclo[3.1.0]hexeno compounds (toxisterols C) constitute the major fraction of the irradiation mixture; in addition, a partly deconjugated 9,10‐seco‐triene (toxisterol D1), two C‐8 spiro compounds (toxisterols A) and a cyclobuteno compound (toxisterol E1) are found. In alcoholic solutions about half of the irradiation mixture consists of three alcohol addition products (toxisterols B) ‐ which, upon chromatography, in part give rise to two conjugated 9,10‐seco‐trienes (toxisterols D2 and D3) ‐ and a reduction product (toxisterol R1); furthermore, three toxisterols A, two toxisterols C and toxisterol D1 are found. Toxisterols A, B and R represent novel types of products in hexatriene photochemistry.