Singlet oxygen addition

Classical chemiluminescence from lucigenin (20) is obtained from its reaction with hydrogen peroxide in water at a pH of about 10 Qc is reported to be about 0.5% based on lucigenin, but 1.6% based on the product A/-methylacridone which is formed in low yield (46). Lucigenin dioxetane (17) has been prepared by singlet oxygen addition to an electron-rich olefin (16) at low temperature (47). Thermal decomposition of (17) gives of 1.6% (47). 

Another interesting oxidative formation of chlorins from porphyrins is the singlet-oxygen addition to protoporphyrin19 (see Section 1.1.2.2.). 

Singlet oxygen addition to the aromatic rings often follows (see Section 9.4.1). 

Singlet oxygen addition to 1,3-diene 84 yielded benzoh/]-l,2-dioxepine 85 upon bubbling 02 through a CCI4 solution of 1,3-diene 84 for 9 days (Equation 21) <2005CJC227>. 

Ketone 8 and the naphthalene homologue can be generated in solution " from singlet oxygen addition to various alkylidenecycloproparenes (Section VLB.2). However, attempts to construct 87 from 5,7-dibromodibenzo[ ,c]cycloheptadienone were unsuccessful " and the only known condensed analogue is 88 that has been matrix isolated prior to photodecarbonylation". ... 

It has been suggested" that the formation of the keto-aldehyde (137) in relatively high yield from the sensitized photo-oxidation of thujopsene (138) can best be explained in terms of a dioxetan intermediate (139), similar examples of which have recently been found in singlet oxygen addition to electron-rich double bonds. An extensive analysis of the products of acid-catalysed rearrangement of thujopsene (138) has been carried out." Under different acid conditions ten products have been isolated and identified these include the known compounds, chami-grene (140), cuparene (141), and widdrol (142 R = H) together with the previously unknown compounds (142 R = Et) and (143)—(148). The authors have put forward a mechanistic scheme to explain the formation of all these compounds based on interconversions of cyclopropylcarbinyl and homoallyl cations. 

In another report Corey and co-workers prepared ( )-LTB (107) as well as ( )-(6E,8Z)-LTB4 (114) and (6E,10Z)-LTB4 (IIS). The former two isomers were prepared as shown in Scheme 5.34. The synthesis relied on singlet oxygen addition to the epoxy alcohol 116, which provided a mixture of epoxy diols (117 and 118). Reductive removal of two epoxides of the mixture and subsequent hydrolysis of the ester gave a mixture of racemic LTB (107) and its 12-epi-isomer (114). 

The relatively efficient cyclisation of monocyclofamesic acid with boron trifluoride etherate to methyl bicyclofarnesate (46) has led to a successful synthesis of drimenin (48) via acid-catalysed lactonisation of the allylic alcohol (47), a product of singlet oxygen addition to (46). It has also been shown that hydride reduction of drimenin to the allylic diol (49) followed by a two-step oxidation procedure yields cinnamolide (39). A Ci antifungal mould metabolite has... 

Rodgers, M.A.J. (1983) Solvent-induced deactivation of singlet oxygen additivity relationship in nonaromatic solvents, J. Am. Chem. Soc., 105, 6201-6205. 

Foote reactivity indices (ft) have been measured for rubrene and 9,10-dimethyl-anthracene undergoing autophotoperoxidation in a range of solvents for which , has been measured. The variation in /3-values (about a factor of 40) is almost entirely due to the solvent dependence of t 0,. Thus = 1// t 0i varies by less than a factor of 2 ( is the singlet oxygen addition rate constant). However, for... 

The second paper d also describes the first reported conversion of the Cj, hormone into the homologated Cjg hormone. This was accomplished by singlet oxygen addition to the C17 compound and in situ reduction of the resultant hydroperoxides with hexamethylphosphoramide. This yielded as the major... 

The stereochemical outcome and scope of the singlet oxygen addition to dienes to give endoperoxides (88) has been studied and... 

Scheme 9.6 [4 -I- 2] singlet oxygen addition to a-terpinene [11] and to cyclopentadiene 26. ...

Scheme 42. Singlet oxygen addition to the furan (108) afforded the peroxide (109) which could be reduced to the diketone (110) and hence, with ethyl diazoacetate, converted into the pyrazolines (111) (Scheme 43). ...

The [2-1-2] cycloadditions to sulflnes have not, as yet, been observed. However, singlet oxygen addition occurs across the C=S bond of sulflnes with formation of ketones and sulfur dioxide. ... 

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