Singlet oxygen cyclohexadiene

Isopropyl-l, 3-cyclohexadiene, singlet oxygen cycloaddition, 262-3 Isopropyl ether, hydrotrioxide formation, 740 7-Isopropylidenenorbomenes,... 

In addition to the parent compound 2, the derivatives 2a, b, the benzo-system 16, the lactone-peroxides 17, and the fused polycyclic derivatives 18 and 19 could be prepared via the singlet oxygen-diimide route. For example, the parent system 2 was obtained in ca. 40% yield by diimide reduction of the stable 1,3-cyclohexadiene endoperoxide in MeOH at 0 °C27,28). Dihydroascaridole 2a and dihydroergosterol endoperoxide... 

On the other hand, carbonyl quenching by polyenyl radicals in PVC has been invoked in order to account for autoinhibition during photooxidative degradation (52). Some workers have mentioned the possibility of singlet oxygen formation in PVC via the quenching of excited polyenes (25,29) or cyclohexadienes (53). 

Scheme 6.85 Formation of l,2-dioxa-3,4-cyclohexadienes (415) by addition of singlet oxygen to conjugated enynes and retrograde dehydro Diels-Alder reaction of415.

Singlet oxygen affords a variety of regio and diastereoselective reactions with chiral allylic alcohols amines - (e.g. substrate 161, Scheme 58) and chiral cyclohexadienes - that are useful for synthetic transformations. For example, the photooxygenation of a chiral allylic alcohol was used recently as the key step in the total syntheses of plakorin 162 and ewawfio-chondrilin (Scheme 58). If the photooxidation... 

Bald and coworkers synthesized four out of the ten possible diastereomers of querci-tols (Scheme 62), some of which are natural products, by using the ene reaction of singlet oxygen as the key step and the commercially available 1,4-cyclohexadiene as starting material. In this fashion, they managed to avoid the use of natural products, or compounds which require many steps to synthesize, employed as starting materials in all previously reported syntheses. 

Cycloadditions of singlet oxygen to particular fused 1,3-cyclohexadienes can be highly diastereoselective, and therefore useful in the total syntheses of some complex natural products. For example, chemically generated 02 effectively and stereoselectively adds to the termini of the 1,3-diene system in 515 to give a single endoperoxide 516 (81%),... 

Cyclohexadiene and singlet oxygen form (103). Most of the important synthetic approaches for 1,2-thiazines use a fragment in which the S-N bond already exists. Syntheses via [4 + 2] cycloadditions constitute a major part of the synthetic repertoire for this class of compounds (CHEC-II(6)370). Thus, pentadiene with TsNSO gives (104) and perfluoro-l,2-thiazine (105) is prepared by the cycloaddition of thiazyl fluoride (FSN) and perfluoro-1,3-butadiene CF2 = CFCF = CF2 (79CC35). 

The earliest examples of such reactions are the hydride transfer from HCO to formaldehyde (Karpas and Klein, 1975), from DNOT as deuteride to (CH3)3B (Murphy and Beauchamp, 1976), from the conjugate base of 1,4-cyclohexadiene to benzaldehyde (DePuy et al., 1978b) and from alkoxide ions to singlet oxygen (Schmitt el al., 1979). 

Salamci, E., Secen, H., Siitbeyaz, Y. and Bald, M. (1997) A condse and convenient synthesis of dl-proto-quercitol and dl-golo-quercitol via ene reaction of singlet oxygen combined with [2 + 4] cycloaddition to cyclohexadiene. Journal of Organic Chemistry, 62 (8), 2453-2457. 

Three typical water-sohible substrates including the polycyclic aromatic hydrocarbon 3, the cyclohexadienic derivative 5 and the olefin 7 were oxidized in order to assess the efficiency of the oxidizing system H202/Ca(0H)2. These substrates represent standard types of singlet oxygen reactions, namely [4 + 2] cycloaddhion and the ene reactioa The dis pearance of the substrates was monitored by HPLC and the products were identified 1 conq>arison with genuine sanq>les, photochemically obtained. E q)erimental conditions aixl results are summarized in Table 1. 

Salamci, E., Secen, H., Sutbeyaz, Y., Balci, M., A Concise and Convenient Synthesis of dl proto Quercitol and dl gala Quercitol via Ene Reaction of Singlet Oxygen Combined with [2 + 4] Cycloaddition to Cyclohexadiene, J. Org. Chem. 1997, 62, 2453 2457. 

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