- A General Synthesis of Aromatic Compounds Carrying Two Neopentyl Groups on Adjacent Positions
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3,4-Dineopentylthiophene (4) was synthesized in a good overall yield starting frm methyl neopentyl ketone. 3,4-Dineopentylthiophene-1,1-dioxide (5a), easily obtainable by oxidation of 4, undergoes Diels-Alder reactions with a variety of acetylenic dienophiles or their equivalent to furnish aromatic compounds carrying two neopentyl groups on adjacent positions.
- Nakayama, Juzo,Yoshimura, Koichi
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- Preparation of Congested Thiophenes Carrying Bulky Substituents on the 3- and 4-Positions and Their Conversion to the Benzene Derivatives
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Highly congested thiophenes, 3,4-di-tert-butyl-, 3,4-di(1-adamantyl)-, 3,4-dineopentyl-, and 3-(1-adamantyl)-4-tert-butylthiophenes (4a-d), were prepared in satisfactory overall yields by intramolecular reductive coupling of 3-thiapentane-1,5-diones (1a-d) followed by acid-catalyzed dehydration of the resulting thiolane-3,4-diols (2a-d). Experimental procedures of this thiophene synthesis are fully described. Oxidation of the thiophenes 4a-d with m-CPBA gave the corresponding thiophene 1,1-dioxides 13a-d in good yields. The Diels-Alder reactions of 13a-d with phenyl vinyl sulfone gave o-di-tert-butyl-, o-di(1-adamantyl)-, o-dineopentyl-, and o-(1-adamantyl)-tert-butylbenzenes (17a-d) directly in high yields with loss of benzenesulfinic acid and sulfur dioxide. The dioxides 13a-d also underwent Diels-Alder reactions with alkynic dienophiles to give the corresponding benzene derivatives carrying two bulky substituents on adjacent positions. Pyridazines 25b,c, carrying bulky substituents on the 4- and 5-positions, were also synthesized through Diels-Alder reaction of 13b,c with PTAD. Dimethylation of the 2- and 5-positions of 13a-d was attained by treatment with strong bases followed by reactions with methyl iodide. The resulting tetrasubstituted thiophene 1,1-dioxides 14a-d reacted with DMAD to give highly congested hexasubstituted benzene derivatives 15a-d in good yields. Finally, structural features of the congested molecules are discussed on the basis of NMR analyses. Typically, the barriers to rotation (ΔH?) about the benzene to the bulky substituents of 15a,c,d were determined to be 8.59, 15.3, and 7.40 kcal/mol, respectively, by NMR total line-shape analysis.
- Nakayama, Juzo,Hasemi, Ryuji,Yoshimura, Koichi,Sugihara, Yoshiaki,Yamaoka, Shoji,Nakamura, Nobuo
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