1,6:7,12-Bismethano annulene

However, a number of stable bridged [14]annulenes have been prepared,192 e.g., frans-15,16-dimethyldihydropyrene (75),193 syn-l,6 8,13-diimino[14]annulene (76),194 and syrt- and anfi-l,6 8,13-bismethano[14]annulene (77 and 78).195 The dihydropyrene 75 (and its diethyl and dipropyl homologs) is undoubtedly aromatic the n perimeter is approximately... 

Protonation of bismethano[14]annulene and its bridged analogs allowed to generate and characterize the corresponding 109 and 110 cations.286 Protonation always occurs at C(7). 

The striking alternation of bond lengths in 7-methoxycarbonyl-aitf(-1,6 8,13-bismethano[14]annulene (70) [1.33—1.49 A] confirms the polyenic... 

Cr(CO)3(CieHi4)] represents a pentahapto-complex (8). The localized double-bond system. The chromium atom makes close contact with only five carbon atoms of the ligand, and these are in the end ring which contains only two double-bonds the five bonded Cr-C distances... 

Intermediates in Reactions.—The desulphurization of thiepins is believed to proceed by ring contraction to a thiiran. Treatment of benzene oxide-oxepin with thiocyanate ion did not yield benzene sulphide-thiepin, but rather gave benzene, possibly by desulphurization of the unstable benzene sulphide. The synthesis of l,6 8,13-bismethano[14]annulene involves extrusion of a sulphur atom via an intermediate thiiran, and the photolysis of 4-phenylisothio-chromene to 3-phenylindene likewise involves a thiiran (Scheme 2). The... 

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