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Two different synthetic concepts led to the formation of 17, 19, and 29, the first structural isomeric benzobis[1,3]oxathiins. Hetero-DielsAlder reactions of diethyl mesoxylate 14 and the open valence isomers of the benzobisthietes 12 and 18 yielded the linear benzobis[1,3]oxathiin 17 and its angular isomer 22, respectively. The isomeric angular system 29 could be obtained by a twofold O,S-acetalization reaction of the dihydroxydisulfanyl compound 27 and acetone (28).

Naphtothietes and Their Application to the Synthesis of Heterocycles The three isomeric naphthothietes 5, 11, and 16 were prepared according to the reaction sequences shown in Schemes 1–3. The final step was in each case a flash vacuum pyrolysis (FVP) of the corresponding mercaptonaphthalenemethanol 4, 9, and 15, respectively. The thiete rings in 5 and 11 can be opened by gentle heating; the ring opening of the isomer 16 possesses a much higher activation barrier. A MNDO calculation of the ΔHf values of 5, 11, and 16 and the open isomers 5′, 11′, and 16′ provides an explanation for the different behavior. Photochemical ring opening represents a useful alternative. The reaction Schemes 4, 6, and 7 reveal the synthetic potential of the naphtho-condensed thietes. Cycloaddition reactions with CC, CO, or CN double bonds lead into the series of differently condensed thiopyrans 17, 18, 24, 25, 26, 3,1-oxathiine 19 and 1,3-thiazines 20, 21.

Oligo(phenyleneethynylene)s 1 are rod-like compounds with undisturbed conjugation. In supplementation of the previously described members of this series 1a−e, with repeating units of up to n = 5, this work contains the preparation of higher oligomers 1f−i (n = 6, 7, 8, 10) through the use of the Sonogashira−Hagihara reaction. Both the absorption and the fluorescence bands showed convergence for increasing values of n, reaching limiting values at the effective conjugation length of nECL = 10. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)