Abstract:The first synthesis of trans-tricyclo[4.2.0.0(1,3)]oct-4-ene (1), an ethenyl bridged spirohexane, was accomplished in four steps starting from Carpino et al. gem-dichloro ketone 6. An X-ray crystal structure of 1 with one substituent was obtained to provide geometry data on this novel ring system and to confirm the stereochemical assignment of the penultimate synthetic intermediate. Tricyclo[4.2.0. 0(1,3)]oct-4-ene is surprisingly stable. It reacts with glacial acetic acid but only slowly at 145 degrees C; the… Show more
“…Low-temperature Wolff−Kishner reduction 12 of 4 via the intermediacy of its hydrazone derivative gave bicyclo[4.2.0]oct-2-ene ( 1 ). Spectral data recorded for 3 and 4 , both known compounds, were in agreement with the literature. , In contrast, compound 1 , while known, , has been subjected to rigorous spectral analysis for the first time. Not only are high-field 1 H NMR chemical shifts consistent with previously reported low-field values, but 13 C NMR data including a DEPT pulse sequence have provided a compelling structure proof for 1 .…”
Section: Resultssupporting
confidence: 76%
“…Syntheses. The synthesis of bicyclo[4.2.0]oct-2-ene ( 1 ), as shown in Scheme , started with the precursor 8,8-dichlorobicyclo[4.2.0]oct-2-en-7-one ( 3 ), which was prepared in moderate yield from 1,3-cyclohexadiene and trichloroacetyl chloride according to a previously published procedure . Dechlorination with zinc in acetic acid 11 afforded bicyclo[4.2.0]oct-2-en-7-one ( 4 ) in 89% yield.…”
At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.
“…Low-temperature Wolff−Kishner reduction 12 of 4 via the intermediacy of its hydrazone derivative gave bicyclo[4.2.0]oct-2-ene ( 1 ). Spectral data recorded for 3 and 4 , both known compounds, were in agreement with the literature. , In contrast, compound 1 , while known, , has been subjected to rigorous spectral analysis for the first time. Not only are high-field 1 H NMR chemical shifts consistent with previously reported low-field values, but 13 C NMR data including a DEPT pulse sequence have provided a compelling structure proof for 1 .…”
Section: Resultssupporting
confidence: 76%
“…Syntheses. The synthesis of bicyclo[4.2.0]oct-2-ene ( 1 ), as shown in Scheme , started with the precursor 8,8-dichlorobicyclo[4.2.0]oct-2-en-7-one ( 3 ), which was prepared in moderate yield from 1,3-cyclohexadiene and trichloroacetyl chloride according to a previously published procedure . Dechlorination with zinc in acetic acid 11 afforded bicyclo[4.2.0]oct-2-en-7-one ( 4 ) in 89% yield.…”
At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.
“…Because the direct conversion of 1,3-cyclohexadiene and methylketene, generated by treatment of propionyl chloride with triethylamine, resulted in compound 4 in only 4−5% yield, we opted instead to initiate the synthesis of 1 from the 8-chloro-8-methylbicyclo[4.2.0]oct-2-en-7-one 14 ( 3 ) precursor (Scheme ). As the latter ketene cycloaddition proceeded in 63% yield and the subsequent zinc reduction in 53% yield, the overall yield of 33% for the two-step sequence was far superior to the one-step variation. 1 Synthesis of 1 …”
[reaction: see text] At 275 degrees C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, si/sr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
“…Tricyclo[4.2.0.0 1,3 ]oct-4-ene (54), a novel structure containing a bicyclo[3.1.0]hex-2-ene substructure with a 4,5-ethano bridge, may be thermally equilibrated with isomer 55 through a sr [1,3] shift at 180-200 °C. 77 For the forward reaction, E a ≈ 31 kcal/mol, a relatively low barrier associated no doubt with the substantial strain energy of the reactant.…”
Section: A Racemic Sample Of Trans-1-(1′-(tert-butyl-2′-(e)d-vinylmentioning
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