1-Chloro-1-fluorobenzocyclopropene

The Cycloproparenes

“…By employing tetrahalocyclopropenes in Diels-Alder cycloadditions with appropriate buta-1,3-dienes (15), the bicycloheptenes 22 are readily available. Dehydrohalogenation is normally effected by employing potassium terf-butoxide in either tetrahydrofuran or dimethyl sulfoxide and with phenyl substituents at the 2-and 5-positions of 22 the requisite gem-dihalocyclopropabenzenes 23a-c are obtained in 70-95% isolated yield (16,17). In the absence of substituents which can stabilize the development of carbanionic character at the 2-and 5-positions of 22 the elimination is not always easy to effect (16), and although cy-…”

“…A significant advantage of this route to gem-dihalocyclopropabenzenes lies in the viability of the products to act as precursors to other 1,1-disubstituted derivatives by way of ionization and replacement (16)(17)(18)(19)(20)(21). For example, 23a has been converted to the hydrocarbon (17), and diethyl and diphenyl derivatives (21). However, these reactions have not been capable of termination at the mono-replacement stage (17,22).…”

“…For example, 23a has been converted to the hydrocarbon (17), and diethyl and diphenyl derivatives (21). However, these reactions have not been capable of termination at the mono-replacement stage (17,22). Indeed, none of the available syntheses of cyclopropabenzenes have yet yielded an isolable 7-monohalo derivative (17,22,23).…”

“…However, these reactions have not been capable of termination at the mono-replacement stage (17,22). Indeed, none of the available syntheses of cyclopropabenzenes have yet yielded an isolable 7-monohalo derivative (17,22,23). Developments in this area can be expected, however, since 23c is now available (17) and ideally suited to hydride ion exchange of the less electronegative 7-halo substituent.…”

Allylic Reactions of Benzocyclopropenes. Discrimination of halogen substituents in 1, 1‐Dihalogenobenzocyclopropenes

“…As an alternative approach to 4 we considered ionization of as yet unknown 1-halogenobenzocyclopropenes (5). In view of the well-documented instability of dihalogenobenzocyclopropenes 1 [6] [7], we turned our attention first to the much more stable 2,5-diphenyl derivatives [8] for obtaining a 1 -halogeno-2,5-diphenylbenzocyclopropene (6) and ultimately 2,sdiphenylbenzocyclopropenium ion (7). Our first approach consisted in aromatization of 1,6,7-trichloro-2,5-diphenylbicyclo [4.1 .O]hept-3-ene (8) available by partial reduction of the Diels-Alder adduct 9 of diphenylbutadiene and tetra-chlorocyclopropene [8].…”