synthesis of 1-Phenyl -1, 2-Cyclohexadiene and 1-(2-Bromocyclohex-2-En-1-Yl)Benzene and Wurtz-Like Condensation Products in the reaction of 1-(2,3-Dibromocyclohex-1-En-1-Yl) Benzene with Zinc

Abstract

The base-catalysed elimination of 1-(2-bromocyclohex-2-en-1-yl)benzene 1 and the zinc-catalysed elimination of 1-(2,3-dibromocyclohex-1-en-1-yl)benzene 9 have been used for the synthesis of 1-phenyl-1,2-cyclohexadiene 2; reaction of 9 with zinc in THF resulted in the formation of two isomeric Wurtz-like condensation products 3 and 4, but the reaction of 1 with t-BuOK gave the allene 2.

1‐Phenyl‐1,2‐cyclohexadiene: Generation, Interception by Activated Olefins, Dimerisation and Trimerisation

“…Tolbert, Johnson et al [4] arrived at merely 20 % yield and characterised 5, which served as precursor of 2 en route to 4, only as being "thermally unstable". Ceylan and Budak [5] described 5 as a colourless liquid, collected in 67 % yield, whereas we isolated colourless crystals with m.p. 44.5-45 8C.…”

“…Ceylan and Budak claimed to have achieved this rearrangement by heating at 150 8C, whereas heating at 180 8C gave rise to biphenyl. [5] In our hands, biphenyl was formed already at much lower temperatures from 5, [9] and 6 could only be obtained by keeping a solution of 5 at room temperature. Previously, 6 was described as being a colourless liquid, [5,9] but we have now isolated colourless crystals with m.p.…”

“…[1] One of them is 1-phenyl-1,2-cyclohexadiene (2), although it was the target of three research groups. In addition to the Würzburg team, some results of which were reported in a review, [1] Tolbert, Johnson et al [4] as well as Ceylan and Budak [5] examined the interAbstract: Four possible precursors of 1-phenyl-1,2-cyclohexadiene (2) were examined, namely, 6,6-dibromo-1-phenylbicycloA C H T U N G T R E N N U N G [3.1.0]hexane, (1a,5a,6a)-6-bromo-6-fluoro-1-phenylbicyclo-A C H T U N G T R E N N U N G [3.1.0]hexane, 1-bromo-2-phenylcyclohexene and 1-bromo-6-phenylcyclohexene. All four compounds could be converted into 2, as demonstrated by the products of the interception of 2 with activated olefins.…”

“…In addition, our 13 C NMR spectroscopic data are severely at variance with the published ones. [5] On the basis of the readily occurring rearrangement of the unsubstituted 6,6-dibromobicycloA C H T U N G T R E N N U N G [3.1.0]hexane [7] and its 1-methyl derivative, [8] it could not be expected that 5 is highly persistent at room temperature. In fact, it can be stored over extended periods only at À30 8C.…”

“…As the mode for the generation of 2, the photolysis or the thermolysis of the potassium salt of 1-chloro-2-phenylcyclohexene was employed. Compound 4 also emerged from the Doering-Moore-Skattebøl reaction of 6,6-dibromo-1-phenylbicycloA C H T U N G T R E N N U N G [3.1.0]hexane (5) in the presence of 1,3-diphenA C H T U N G T R E N N U N G ylisobenzofuran. [4] The Turkish group [5] treated 1-bromo-2-phenylcyclohexene (8) with potassium tert-butoxide (KOtBu), but obtained only rather indirect evidence in favour of the intermediate 2 (see below).…”