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Organic Lab Reactions 128

Organic Lab Reactions 128 - 25 The ori-entation influence...

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STERIC FACTORS OTHER THAN RING SIZE 123 Some of the other conventional methods of ring closure, moreover, failed to give any of the ketone XXXVIII. 26 XXXIX (H, - ED XL (R - CHj) CH, The only cases of cyclization of 7-2-naphthylbutyric acids in which the ring does not close into the reactive 1-position to form a phenanthrene derivative are those in which either this position is blocked or the 8-posi- tion is substituted. The latter clearly seems to be an example of hin- drance. An illustration is afforded by the cyclization of Y-8-methyl-2- naphthylbutyric acid (XXXIX) to the linear anthracene derivative XLI instead of the expected ketotetrahydrophenanthrene.
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Unformatted text preview: 25 The ori-entation influence of the methyl substituent would not be expected to affect the course of the reaction in such a manner. In like manner the tetramethyl derivative XL gave the product of linear ring closure XLII in good yield. 27 A similar abnormal course of cyclization 28 has been observed in the benzylbenzoic acid derivative, o-(8-methyl-2-naphthyl-* methyl)-benzoic acid (XLIII) to give the linear benzanthrone XLIV. / 28 Fieser and Bradsher, J. Am. Chem, Soc, 68, 1738 (1936). 27 Hewett, J. Chem. Soc., 1940, 293. 28 Fieser and Hershberg, J. Am. Chem. Soc., 62, 49 (1940)....
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