Cyclic acetylenes large-ring

The reaction of 1,2-dibromocycloalkenes (13) with magnesium in the presence of l,3-diphenylbenzo[c]furan (16) affords a cycloalkyne adduct (17). Also, the mercuric oxide oxidation of bishydrazone, which has been used extensively in the preparation of open-chain and medium or large cyclic acetylenes " , is adapted for small ring bishydrazones (18) . Treatment of 18 with mercuric oxide in the presence of 16 or of phenyl azide results in the adducts, 17 and 19, respectively. It seems... 

A large number of cyclic acetylenes have been synthesized to investigate the proximity interactions between two triple bonds or between a triple bond and other unsaturated systems. Such transannular proximity interactions have been observed in some cyclic acetylenes of medium ring size. However, no appreciable evidence of the interaction was detected in the electronic spectra of diacctylenes 1 2 - and 3... 

Meier has provided an excellent review of medium- and large-ring cyclic acetylenes. Cycloheptyne and cyclo-octyne may be obtained by pyrolysis of (144 n = 7 or 8), which can be readily obtained by selenium dioxide oxidation of the corresponding semicarbazones the photochemistry of cyclo-octyne in the presence of molybdenum hexacarbonyl is discussed. Compound (145) reacts with sodium methoxide to give (146) the acetylene (147) is proposed as an intermediate. 

The spiro quinoline formation was applied to a large-membered ring. The substrate 39,bearing a 15-membered ring cyclic olefin and a terminal acetylene was cyclized under the previously described conditions to give the olefin migration product 40 in a moderate yield (53%) but good enantioselectivity (86% ee) (Scheme 29). 

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