Vitamin conjugated triene system

Vitamin D. The term vitamin D refers to a group of seco-steroids that possess a common conjugated triene system of double bonds. Vitamin I), (10a) and vitamin D, (10b) are the best-known examples (Fig. 2). Vitamin D (10a) is found primarily in vertebrates, whereas vitamin 11 (10b) is found primarily in plants. The term vitamin is a misnomer. Vitamin I) is a prohormonc that is converted into physiologically active form, primarily 1.25-dihydroxy vitamin D3 (11), by successive hydroxylalions in the liver and kidney. This active form is part of a hormonal system that regulates calcium and phosphate metabolism in the target tissues. 

In the construction of the conjugated triene system 177 in vitamin D, the intermolecular insertion of the terminal triple bond of the 1,7-enyne 175 to the alkenylpalladium, formed from 174, occurs at first to form the alkenylpalladium 176. Further intramolecular insertion of the terminal double bond in 176, followed by fi-elimination yielded the triene system 177 in 76% yield [77]. 

Vitamin D refers to a group of seco-steroids that possess a common conjugated triene system of double bonds. Vitamin [67-97-0] (16a) and vitamin D2... 

An important group of conjugated diene/triene systems are those in the vitamin D series. The key reactions in the commercial manufacture of vitamin D (and probably also in its formation in skin exposed to daylight) are a photochemical, conrotatory electrocydic ring-opening in the provitamin, and a thermal 1.7-shift of hydrogen in the previtamin so formed (2.23). High conversions to the vitamin are not normally possible because all three species absorb appreciably at the... 

It is an interesting historical fact that the study of the photochemistry of conjugated dienes and trienes was initiated by the discovery of the photochemical transformation of ergosterol to vitamin D—a system... 

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