Organic Lab Reactions 129

Organic Lab Reactions 129 - 10-so-M XT.TT DIRECTION OF RING...

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124 THE FORMATION OF CYCLIC KETONES A different type of steric interference is revealed by the resistance to formation of certain types of polycyclic ring systems. The hydrindenyl- acetic acid XLV could not be cyclized, 29 even though the five-membered ring might be expected to close. Moreover, all attempts to induce the acids XLVI 30 and XLVII 31 to undergo cyclization resulted only in the formation of intermolecular condensation products. CO 2 H H2CO2H XLV 3XYI xx,vn xivm All these product's of cyclization would contain two fused five-membered rings mutually fused to a benzene nucleus. This structure, formula XLVIII, represents a highly strained system. On the other hand, the basic polycyclic structures represented by formulas XLIX through LII can be formed by the intramolecular acylation reaction.
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Unformatted text preview: 10-so-M XT.TT DIRECTION OF RING CLOSURE The Benzene Nucleus. The main problem in direction of cyclization is presented when both positions ortho to the acid side chain are available and ring closure into both would result in the formation of two isomerie ketones. In the benzene series the only acids having these structural properties are the meta substituted phenylbutyric and phenylpropionic acids, with which cyclization usually takes plaee at the position para to the substituent. Thus 6-methoxytetralone-l (LIV) was obtained u " v . Brauft, Danziger, and Koehler, Ber., 60, 56 (1917). \ 30 v. Braun and Rath, Ber., 61, 956 (1928). 81 v. Braun and Anton, Ber., 62, 145 (1929). 82 v. Braun and Reutter, Ber., 69, 1922 (1926)....
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