Singlet Oxygen-Mediated Allylic Oxidation

Authored by: Mariza N. Alberti , Michael Orfanopoulos

CRC Handbook of Organic Photochemistry and Photobiology

Print publication date:  March  2012
Online publication date:  March  2012

Print ISBN: 9781439899335
eBook ISBN: 9781466561250
Adobe ISBN:

10.1201/b12252-32

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Abstract

The chemistry of singlet molecular oxygen (1O2) 1 has attracted continuous and remarkable attention for its synthetic, 2 mechanistic, environmental, 3 as well as therapeutic applications. 4 In 1931, Kautsky first demonstrated the importance of a “reactive oxygen molecule” in dye-sensitized photooxidation reactions. 5 However, Kautsky’s pioneering work and careful reasoning were largely ignored for many years. Later on, Foote and Wexler 6a provided new experimental evidence for the involvement of 1O2 as the reactive intermediate in photochemical processes in solution. 6 This breakthrough brought 1O2 into the mainstream of chemical research. The reaction of 1O2 with C=C bonds can be classified into three fundamental categories: (1) conjugated dienes react preferably by [4 + 2] cyclo-addition to yield endoperoxides; 7 (2) electron-rich alkenes, without allylic hydrogen atoms of proper orientation, react by [2 + 2] cycloaddition to form 1,2-dioxetanes 7c,8 and (3) inactivated alkenes bearing allylic hydrogen atoms react via the so-called ene or Schenck 9 reaction yielding allylic hydro-peroxides. The latter reaction type has arguably drawn the most extensive experimental as well as theoretical attention. 10 Notably, this reaction has been applied toward the synthesis of several natural products 11 as well as 1,2,4-trioxanes. 12 Moreover, the allylic hydroperoxides that have been obtained from this reaction can be further transformed to useful target molecules such as allylic or epoxy alcohols and enones.

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