Solar reactions for preparing hindered 7-cis-isomers of dienes and trienes in the vitamin A series

Abstract

Selective triplet sensitized isomerizations of dienes and trienes in the vitamin A series were accomplished through solar irradiation. The use of Rose Bengal as a photosensitizer for triene derivatives allowed the tapping of the visible region of the sunlight, thereby making a rapid conversion to the desired hindered 7-cis isomers possible. The short exposure time has led to the design of a simple floating solar reactor that eliminated the need of circulating cooling water. That such a very green approach to photochemical reactions could be carried out in a single surfing session, while using the Pacific Ocean as the heat sink, has added an obvious fun component to the photochemical project. Conversion to 7-cis-β-ionol was quantitative, albeit at a slower rate because of the need to use a colorless photosensitizer.