Sensitized photooxidation of a model 1,4‐diene, 4cis, 7cis‐undecadiene, was shown to yield 4‐hydroperoxy‐5trans,7cis‐undecadiene and 5‐hydroperoxy‐3trans,7cis‐undecadiene as initial products. Further irradiation (in the presence of the sensitizer) caused the isomerization of 4‐hydroperoxy‐5trans,7cis‐undecadiene to 4‐hydroperoxy‐5trans,7trans‐undecadiene. Oxidation of 4cis,7cis‐undecadiene with chemically formed singlet oxygen gave the same initial products as the photosensitized oxidation. 5‐Hydroperoxy‐3trans,7cis‐undecadiene is, however, not formed in the radical autoxidation of the diene. It is concluded that singlet oxygen is the reactive intermediate in the photooxidation. Comparison with this model reaction suggests that the photooxidation of refined soybean oil in propanol also proceeds via singlet oxygen: the photooxidations of both 4,7‐undecadiene and soybean oil are inhibited by β‐carotene and by triethylamine, but unlike radical chain autoxidation, they are not inhibited by 2,6‐di‐t‐butyl‐4‐methylphenol. Also soybean oil can act as a sensitizer for the photooxidation of 4,7‐undecadiene. Chlorophyl‐like sensitizers are probably unimportant in the well refined soybean oil used in this work. The observed photooxidation of the skipped dienoic components of soybean oil, which is probably due to some other, unidentified sensitizer(s), absorbing below 500 nm, can be avoided by using a yellow filter.

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The Diels-Alder reactions of 1 -(p-substituted phenyl) buta-1.3-dienes with methyl acrylate are shown to give 2-arylcyclohex-3-enecarboxylates, irrespective of the nature of the aryl-substituent, but the steric course of the reaction is affected by the substituent. Similar results were obtained with 1 -aryl-2,3-dimethylbuta-l,3-dienes. THE Diels-Alder reaction is highly structurally specific and stere0specific.l The reaction of a l-substituted diene (1) with methyl acrylate can give rise to two structural isomers, the ' ortho-isomer ' (2) and the ' metaisomer ' (3), each of which can exist in cis-and transforms. In general the ' ortho-isomer ' is the major product, and often the only one isolated. Many reported ortho-meta isomer ratios are dependent on isolation procedures and are therefore not necessarily accurate. We now report a gas chromatographic examination of the reactions between the l-(#-substituted phenyl) butadienes (la-c) and methyl acrylate.The reaction between l-phenylbuta-lJ3-diene and methyl acrylate at 150" has been examined by Nazarov, Titov, and Kuznetsova who found that the ortho-and meta-adducts (2a) and (3a) were formed in the ratio of 95.5: 2-5. This ratio was determined by isolation of the known biphenylcarboxylic acids. The cis-trans ratio of the ortko-isomers was found to be 89 : 11 by degradation to the known cis-and trans-2-phenylcyclo-For references to Diels-Alder reaction see ref. 1 of preceding paper.

A number of Diels-Alder reactions between 1 -phenyl-, 1 -p-methoxyphenyl-, and 1 -p-nitrophenyl-2.3-dimethylbutadiene and methoxycarbonyl-, 2.6-dimethyL.2.5-dimethyl-, 2-methoxy-6-methyl-, 5-methoxy-2-methoxycarbonyl-3-methyl-, and 2-cyano-3.5-dimethyl-p-benzoquinone are reported. The structures of the major products are established and their formation is interpreted on the basis of a transition state having some diradical character.

Die Diels‐Alder‐Reaktion der Butadiene (Ia) mit dem Ester (II) liefert fast ausschließlich die Addukte (IIIa).