1121-10-4Relevant academic research and scientific papers
Modular Entry to Functionalized Tetrahydrobenzo[ b]azepines via the Palladium/Norbornene Cooperative Catalysis Enabled by a C7-Modified Norbornene
Dong, Guangbin,Liu, Xin,Wang, Jianchun
, p. 9991 - 10004 (2021)
Tetrahydrobenzo[b]azepines (THBAs) are commonly found in many bioactive compounds; however, the modular preparation of functionalized THBAs remains challenging to date. Here, we report a straightforward method to synthesize THBAs directly from simple aryl iodides via palladium/norbornene (Pd/NBE) cooperative catalysis. Capitalizing on an olefin-tethered electrophilic amine reagent, an ortho amination followed by 7-exo-trig Heck cyclization furnishes the seven-membered heterocycle. To overcome the difficulty with ortho-unsubstituted aryl iodide substrates, we discovered a unique C7-bromo-substituted NBE (N1) to offer the desired reactivity and selectivity. In addition to THBAs, synthesis of other benzo-seven-membered ring compounds can also be promoted by N1. Combined experimental and computational studies show that the C7-bromo group in N1 plays an important and versatile role in this catalysis, including promoting β-carbon elimination, suppressing benzocyclobutene formation, and stabilizing reaction intermediates. The mechanistic insights gained could guide future catalyst design. The synthetic utility has been demonstrated in a streamlined synthesis of tolvaptan and forming diverse pharmaceutically relevant THBA derivatives. Finally, a complementary and general catalytic condition to access C6-substituted THBAs from ortho-substituted aryl iodides has also been developed.
Unexpected interconnection of the 7-norbornenyl and 3-nortricyclcyl/5- norbornen-2-yl cations
Moss, Robert A.,Fu, Xiaolin
, p. 5321 - 5324 (2007/10/03)
Fragmentation of syn-7-norbornenyloxychlorocarbene provides products derived from both 7-norbornenyl cation-chloride anion pairs and from 3-nortricyclyl/2-norbornen-5-yl cation-chloride anion pairs. A 5,7-hydride shift within the 7-norbornenyl cation is proposed to interconnect the two cation systems.
Influence of carbocation stability in the gas phase on solvolytic reactivity: Beyond bridgehead derivatives
Abboud, Jose-Luis M.,Alkorta, Ibon,Davalos, Juan Z.,Mueller, Paul,Quintanilla, Esther,Rossier, Jean-Claude
, p. 3786 - 3796 (2007/10/03)
The intrinsic gas-phase stability of bicyclic secondary carbocations has been determined by Dissociative Proton Attachment of chlorides and alcohols, respectively. From these data, Gibbs free energies for hydride transfer relative to 1-adamantyl (ΔrG°(8,exp)) are derived after application of appropriate leaving group corrections, and good agreement with theoretical values, (ΔrG°(8,comp)), calculated at the G2(MP2) or MP2/6-311G(d,p) level, is reached (Table 1). The relative rate constants for solvolysis (log(k/k0)) of the bicyclic secondary derivatives correlate with the stabilities of the respective carbocations in the same manner as tertiary bridgehead derivatives, but simple monoderivatives and acyclic derivatives solvolyze faster than predicted on the grounds of the ion stabilities. The corresponding stabilities of cyclopropyl- and benzyl-substituted carbocations have been obtained by a combination of experimental and computational data available in the literature with computational methods. Correlation of the rate constants for solvolysis vs ion stabilities for these compounds reveals a trend similar to that observed for bridgehead derivatives, but with much more scatter, which is attributed to nucleophilic solvent participation and/or nucleophilic solvation.
Solvolysis of tricyclo[4.1.0.02,7]hept-4-en-3-yl and tricyclo[4.1.0.02,7]hept-3-yl methanesulfonates and p-nitrobenzoates - Remarkably small enthalpy difference between the C7H7 cations tricyclo[4.1.0.02,7]hept-4-en-3-yl and 7-norbornadienyl
Bentley, T. William,Llewellyn, Gareth,Norman, Simon J.,Kemmer, Ralf,Kunz, Ulrike,Christl, Manfred
, p. 229 - 244 (2007/10/03)
In an extension of previous work, tricyclo[4.1.0.02,7]heptan-3-ol (5) was synthesised in four steps from benzvalene. Methanesulfonates 12 and 6b, c, prepared from 5 and 4-halotricyclo[4.1.0.02,7]hept-4-en-3-ols 4b, c, were too unstable to be isolated, but were unambiguously characterised by their NMR spectra. On treatment of the unsubstituted tricycloheptenol 4a with methanesulfonyl chloride, the expected mesylate 6a could not be observed. Even at -40°C, only its consecutive products 3-chlorotricyclo[4.1.0.02,7]hept-4-en (7a) and 7-chloronorbornadiene (8a) were discernible. The analogous reaction of 6b occurred only at room temperature, with formation of the dichlorotricycloheptene 7b and the dichloronorbornadiene 8b. Rearrangement products of 6b and 12 were the chloronorbornadiene mesylate 10b and anti-7-norbornenyl mesylate (13), respectively. - The solvolysis of 6b, c in aqueous ethanol and of 6b in 2,2,2-trifluoroethanol (TFE) gave nonrearranged products exclusively, i.e. the alcohols 4b, c, the ethyl ethers 17b, c, and the trifluoroethyl ether 18b. In contrast, from 12 only rearranged products arose, namely anti-7-norbornenol (30) and its ethyl ether 31. The solvolysis of the unsubstituted tricycloheptenyl p-nitrobenzoate 11a in 80% aqueous ethanol proceeded about equally fast in parallel reactions with cycloalkyl-oxygen and acyl-oxygen cleavage. In addition to the tricycloheptenol 4a, the tricycloheptenyl ethyl ether 17a, ethyl 7-norbornadienyl ether (19), 7-norbornadienyl p-nitrobenzoate (20), and ethyl p-nitrobenzoate were formed. No acyl-oxygen cleavage took place in TFE as solvent, where the tricycloheptenyl trifluoroethyl ether 18a, 20, 7-norbornadienyl trifluoroethyl ether (21), and the cyclopentadienylvinyl trifluoroethyl ethers 22/23 were produced. A new mechanism is proposed for the route to the major products 22/23 via the intermediate 7-norbornadienyl cation (9a), which was attacked by TFE at the two-membered bridge stabilising the positive charge. Thus formed, tricyclo[3.2.0.02,7]hept-3-en-endo-6-yl trifluoroethyl ether (24) underwent a Diels-Alder cycloreversion generating the cyclopentadienylvinyl trifluoroethyl ether 25, the immediate precursor of 22/23. - From kinetic data for these processes and thermochemical data for appropriate hydrocarbons, the enthalpy difference between the C7H7 cations, tricyclo[4.1.0.02,7]hept-4-en-3-yl (3a) and 7-norbornadienyl (9a), was calculated to be only 8 kcal mol-1. VCH Verlagsgesellschaft mbH, 1997.
