Subject allene oxides

The photodegradation and photo-oxidation of polymer systems is still a subject of considerable scientific and technological activity. A number of general review articles have appeared on the subject. Allen and McKellar " have reviewed the interactions of light with polymers, and Shalaby has written a comprehensive review on all the chemical, physical, and environmental aspects of polymer photodegradation. Three other reviews of interest have also appeared. ... 

Peroxidation of lipids is another factor which must be considered in the safety evaluation of liposome administration. Smith and coworkers (1983) demonstrated that lipid peroxides can play an important role in liver toxicity. Allen et al. (1984) showed that liposomes protected by an antioxidant caused less MPS impairment than liposomes subjected to mild oxidizing conditions. From the study of Kunimoto et al. (1981) it can be concluded that the level of peroxidation in freshly prepared liposome preparations and those on storage strongly depends both on the phospholipid fatty acid composition and on the head group of the phospholipid. Addition of appropriate antioxidants to liposomes composed of lipids which are liable to peroxidation and designed for use in human studies is therefore necessary. 

When propargylamine 183 was subjected to a homologative allenylation (Crabbe reaction) at 100 °C, the resulting allene underwent a spontaneous Diels-Alder reaction to give the adduct 184. This intramolecular cycloaddition-oxidation sequence provided a simple route to indole alkaloids such as hippadine and ds-trikentrin B [148]. 

Sengar and Guptaclaim that the silver ion-catalysed oxidation is subject to inhibition by oxalate, and they report other features not noticed by Kalb and Allen. Sengar and Gupta do not mention any control of the amounts of copper and oxygen in their solutions, and possibly their results were affected by the presence of these substances. 

Cyclic allenes have also been subjected to DMD oxidations (Scheme 25). Treatment of 1,2-cyclononadiene (126) with DMD affords the corresponding stable dioxide (127) exclusively <9lJOCH53> on the other hand, MCPBA oxidation of (128) leads to an unstable monooxide (129) which gives (130) via rearrangement to the corresponding cyclopropanone and CO loss <9iJOC6372>. 

The proposed mechanism based on product observation is depicted in (Scheme 16). Regioselective insertion of the proximal double bond of allene 31 into the Si-[Rh] bond of the hydrosilane-[Rh] oxidative adduct, HlRhJSiRs, affords intermediate D-L Subsequent allqme insertion forming the cyclic vinyl-Rh complex D-II followed by silane promoted reductive elimination provides the product 32 and the active Rh-Si complex. When allenynes that did not have substitutions on the alkyne terminus or on the distal allene double bonds were subjected to the optimized conditions, complex product mixtures were obtained. These... 

Although the homogeneous catalytic activity of metal clusters has been recently the subject of a series of investigations [100], direct evidence that a real metal cluster cage is maintained as such under catalytic conditions is lacking in most cases. However, the recent work done with clusters as Ni4(CNR)7 [149], Rht(CO)ie [150,151], or Ru3(CO)i2 [152] has shown that small clusters can display, under particular conditions, catalytic activity in reactions such as cyclisation of acetylene and butadiene [149], polymerization of allene [149], oxidation of ketones [150], oxidation with O2 of CO to CO2 [150], conversion of hydrogen and carbon monoxide to methanol... 

The reaction may also be intramolecular. The allenic ether 6.28 was subjected to Wacker conditions, employing benzoquinone as the oxidant, on a multigramme scale (Scheme 6.13)." The palladium could catalyse both the hydrolysis of the allenic ether to enone 6.29 and the 6-endo cyclization to the tetrahydropyran 6.30. In contrast, use of Brpnsted acids to catalyse the cyclization of the isolated enone resulted in partial epimerization. ... 

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