effected, albeit slowly. After destruction of the latter using 1:1 (v/v) tetrahydrofuran/4 M aqueous hydrochloric acid (vide ante), 595 mg (84%) of a mixture was obtained and shown by VPC analysis (6 ft X 0.125 in. Carbowax 20M column; oven temperature 138 °C; retention times: ketone, 2.0 min; alcohol, 2.4 min) to consist of 2-methylcyclohexanol and the corresponding ketone in an 85:15 ratio. The alcohol and ketone were further identified by coinjection with known samples of each compound. Subsequent NMR analysis (C/fOH signals) indicated that the alcohol product was a 1:1 mixture of cis:trans stereoisomers.
A study of the synthesis and keto-enol tautomerism in a naphtho and several anthrathiophene systems was undertaken with the objective of determining the structural features which influence the position of equilibrium in these fused systems. Thus 4,[3][4][5][6]thiophen-4-one (3) and 4,ll-dihydroanthra[2,3-6]thiophen-ll-one (4) were synthesized and studied spectroscopically. Difficulties in the attempted synthesis of 4,ll-dihydroanthra [2,3-c]thiophen-4-one (5) prompted the synthesis of l,3-dimethyl-4,ll-dihydroanthra[2,3c]thiophen-4-one (6). This modification necessitated the synthesis of l,3-dimethyl-4,9-dihydronaphtho[2,3-c]thiophen-4-one (7) so that comparisons with the naphthothiophene system could be made. It was found that the c-fused ketones 6 and 7 gave no evidence of the presence of enolic material when their NMR spectra were studied in CDC13 or MejSO-dg. A solution of 3 in CDC13 or CDC13-CF3C02H gave no NMR spectroscopic evidence of enolic material on standing. In Me^O-dg only enolic material appeared to be present. In the case of 4 a freshly prepared solution in CDC13 showed only keto form, but when the solution was allowed to stand for 96 h, the NMR spectrum of the solution showed a 33% enol content. In CDC13-CF3C02H at equilibrium a 39% enol content was observed. It is concluded that in these systems c fusion of a thiophene ring predisposes the compound to exist exclusively in the keto forms (6k,7k) since this avoids the intermediacy of the unstable anthra[c]-and naphtho[c]thiophenes. b fusion of a thiophene ring permits varying amounts of enol in the cases of 3 and 4, depending on the solvent.
Naphthalin‐Z,3‐dicarbonsäureanhydrid (I) reagiert mit Thiophen (II) unter Friedel‐ Crafts‐Bedingungen zum Keton (IIIa), das nach Reduktion zu (IIIb) mit Phosphorpentachlorid zum Keton (IV) cyclisiert und weiter zu (V) acetyliert wird.
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