Synthesis and reactivities of a highly strained thiophene with two fused four-membered rings, 1,2,4,5-tetahydrodicyclobuta[b,d] thiophene

Article abstract of DOI:10.1021/ja00064a024

The successful synthesis of 1,2,4,5-tetrahydrodicyclobuta[b,d]thiophene (1) and its ususually enhanced reactivities because of large ring strain are described. Thus, intramolecular pinacol coupling of diketo sulflde 14, obtainable from 2-bromocyclobutanone and sodium sulfide, with a low-valent titanium reagent affords the thiolane3,4-diol 15 in 36% yield based on the bromo ketone. After conversion of 15 to the bis-methanesulfonate 16 in 66% yield, the latter was treated with potassium tert-butoxide to give 1 nearly quantitatively as a rather thermally stable, colorless, highly sublimative, nicely crystalline compound. Bromine rapidly adds to 1 to give the tetrabromide 21, revealing its olefinic character. Furthermore, 1 undergoes Diels-Alder reaction with tetracyanoethylene at room temperature to afford the adduct 22 in 83% yield. The Diels-Alder reaction with maleic anhydride at room temperature gives the adduct 23 in 87% yield in the endo-exo isomer ratio 5:1, whereas the reaction with excess maleic anhydride in refluxing benzene produces the bisadduct 24 in 84% yield with loss of sulfur. Similar behaviors of 1 toward N-phenylmaleimide were also observed. Flash vacuum pyrolysis of 1 gave benzo[b]thiophene in 16% yield but not the expected radialene 11 or its dimer, superthiophenophane. Other attempts to obtain 11 or to trap it with a dienophile were also unsuccessful.

Full text of DOI:10.1021/ja00064a024

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.