Photooxygenation (O-1(2)) Of ortho-prenylphenols followed by a reduction (PPh3) at low temperature (-30 degrees C) yields a mixture of ortho-(2-hydroxy-3-methylbut-3-enyl)phenols and ortho-(3-hydroxy-3-methyl-but-1-enyl)phenols. However, by running the two-step sequence at a higher temperature (15 degrees C), the secondary allylic alcohol could be selectively recovered. (C) 2000 Elsevier Science Ltd. All rights reserved.
Regioselectivity in the ene reaction of singlet oxygen with ortho-prenylphenol derivatives
The ene reaction of singletoxygen with prenylated dihydroxyacetophenones led to the 2-hydroperoxy-3-methylbut-3-enyl derivatives as the major product. This original regioselectivity outlined a new effect, in competition with the previously established large group non-bonding effect. The oxidation products distribution could be explained by a stabilising interaction between the phenolic hydrogen, ortho