Anions cycloproparenyl

An overview on cycloproparenyl anions has also been reported.3 According to theoretical calculation, cyclopropabenzenyl anion is by ca 145 kJmol-1 more stable than the parent cyclopropenyl anion. It has been shown that the stability of the cyclopropabenzenyl anion could be considerably enhanced by substitution of the aromatic ring with fluorine and cyano groups, and also by a linear extension of the aromatic backbone. 

Despite the paucity of data for 9 itself, there now exists a wide range of derivatives in the cyclopropabenzene and -[Z ]naphthalene series that have been expanded upon since a 1987 accountThe preparation of these derivatives can be effected by one of three distinct routes depending upon the particular nature of the compound sought. Each has its limitations and none has provided a parent methylenecycloproparene. The first method depends upon the availability of the cycloproparenyl anion (Section IV.B) which can be intercepted by trimethylsilyl chloride to give silane 93 (R=H). In turn, deprotonation of 93 at the benzylic position affords the stabilized a-silyl anion that gives alkylidene derivatives 94 (R=H) from interaction with an appropriate carbonyl compound in a Peterson olefination (Scheme 12). The reaction sequence can be effected as a one-pot operation... 

As the methylene protons of the cycloproparenes are formally benzylic, the compounds should be at least as acidic as the corresponding methyl arenes. Simple extended Huckel calculations concur and predict some stabilization of 6 from charge delocalization the cycloproparenyl anion (6) is expected to be accessible. Indeed, treatment of 1 with butyl-lithium at -78 °C provides an organolithium that has been characterized by NMR and shown to be monomeric in solution. Both the H NMR (H(d 1.91, H(2/s) 5.83, H(3/4) 6.13 ppm, respectively) and NMR (C(,) 31.3, C(,a/5a) 149.0, 99.1, C(3/4) 120.4 ppm, respec-... 

The formal removal of a C(l) substituent as anion, cation or radical from a cycloproparene provides the counter cycloproparenyl species 5-7 and suggestions on the existence of such entities predate the establishment of the cycloproparenes as a viable class of compounds6 0. 

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