From Allenes to Tetracenes: A Synthetic and Structural Study of Silyl‐ and Halo‐Allenes and Their Dimers Journal Articles uri icon

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abstract

  • Abstract9‐Alkynylfluoren‐9‐ols of type C13H8(OH)–C≡C–R, where R is phenyl (1a), p‐tolyl (1b), p‐methoxyphenyl (1c), or trimethylsilyl (1d), react with HBr to yield the corresponding bromoallenes C12H8C=C=C(Br)R (13a–d). Lithiation and hydrolysis of 13d yields 3,3‐(biphenyl‐2,2′‐diyl)‐1‐(trimethylsilyl)allene (20), which forms successively the head‐to‐tail dimer 1‐(9‐fluorenylidene)‐4‐(trimethylsilyl)‐2‐[(trimethylsilyl)methylene]spiro[cyclobutane‐3,9′‐[9H]fluorene] (21) and the tail‐to‐tail dimer trans‐3,4‐bis(trimethylsilyl)‐1,2‐di(fluorenylidene)cyclobutane (23) both of which exhibit long (ca. 1.6 Å) C(3)–C(4) bonds. Treatment of 21 and 23 with TBAF brings about desilylation to 22 and 24, respectively. In the latter case, removal of the bulky trimethylsilyl groups reduces the C(3)–C(4) bond length in 1,2‐di(fluorenylidene)cyclobutane (24) to a more normal value of 1.547 Å; however, the large wingspan of the severely overlapping fluorenylidene moieties retains the C2 symmetry of the system. Prolonged exposure to sunlight of the disilylated head‐to‐tail dimer 21 results in homolysis of the long C(3)–C(4) bond, generation of a peroxide, and ultimately formation of the lactol 25. X‐ray crystallographic data are reported for, among others, 1c, 13a, 21, 22, 23, 24, 25, and also for 3,3‐(biphenyl‐2,2′‐diyl)‐1‐chloroallene (12).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

publication date

  • June 2007