Dithia- phane

The application of reaction conditions as optimized in the preparation of the dithia[2.2]phane 88 allowed Meurer and Vogtle [83] to synthesize the first helically chiral dihetera[2.2]metacyclophanes 91 and 92 in 1.9 and 9% yield. It was impossible to isolate these cyclophanes in all the previous attempts where cesium salts had not been applied [84, 85]. 

Vogtle and Klieser [86] succeeded in the first four-(and fivefold) bridging of the benzene ring by cyclization of tetrakis(bromomethyl)benzene (93) with the corresponding tetrathiol 94. Whilst the combination CS2CO3/DMF led to the isomeric phanes 97 in a total yield of 10%, cyclizations with other solvent/base combinations such as e.g. K2CO3/DMF only produced the dithia compound 98 [86]. 

Hossain, M.K., Takeshita, M., and Yamato, T. (2005) Synthesis, stmc-ture, and photochromic properties of dithia(dithienylethena)phane derivatives. Eur. J. Org. Chem., 13, 2771-2776. 

Although the mechanism of the photoisomerization of azobenzene may involve either twisting around the central NN double bond in the excited state (rotation mechanism) or inversion at one of the nitrogen atoms (inversion mechanism), this has been a subject of debate. Evidence has recently been reported for the involvement of an inversion mechanism for me excitations. An ,Z-photoisomerization took place when -2,19-dithia[3,3](4,4 )-tra s-diphenyldiazeno(4)phane 1 in benzene was irradiated. This... 

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