Strained bridgehead double bonds

Warner, Philip

doi:10.1021/cr00095a007

Cited by 166 publications

(81 citation statements)

References 60 publications

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“…Thus, in this case, single-electron ionization is less costly and the difference in Koopmans' ionization energies works towards the increasing basicity of 5, which together with second largest relaxation energy of all compounds investigated here, makes this molecule the strongest base within this family of molecules (1)(2)(3)(4)(5). At the end, it is useful to emphasize that triadic analysis clearly reveals not only that the correct trend in basicity of systems 2-5 cannot be explained by considering only the features of initial bases, but also that, in all four cases, both properties of different states and their diverse relative significance are factors governing their basicities.…”

Section: Resultsmentioning

confidence: 83%

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Radić¹,

Despotović²,

Vianello³

2012

Croat. Chem. Acta

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Abstract. M06-2X/6-311++G(2df,2pd)//M06-2X/6-31+G(d) computations were employed to investigate the intrinsic gas phase basicity of strained nitrogen heterocycles involving aziridine, azetidine, pyrrolidine and piperidine, together with their N-methyl and N-phenyl derivatives, NR(CH 2 ) n (n = 2-5; R = H, Me and Ph). Basicity constants were compared with the corresponding acyclic counterparts, NR(CH 3 ) 2 (R = H, Me and Ph), and were, based on triadic analysis, resolved into contributions mirroring features of both initial base and the final protonated form as well as their interplay, thus offering quantitative insight into the obtained results. In general, the N-methyl derivatives provided strongest bases investigated here, and, within each group of molecules, the basicity increased on going from three-to six-membered rings, consistent with a decrease in ring strain, with four-membered systems already surpassing or coming close to the basicity of the acyclic gauge molecule. Calculated basicities were found in a very good agreement with available experimental data, except for N-methylazetidine, where a remarkable discrepancy was revealed, suggesting that this system should be experimentally reassessed and its gas-phase basicity parameters revised. Triadic analysis showed different behaviour of individual contributions governing basicities, both among and within distinct families of molecules. It also convincingly demonstrated that, if a proper and a quantitatively accurate interpretation of observed basicity trends is desired, one should not rely only on concepts such as localized reactive hybrid orbitals (RHO) or thus derived nitrogen electron-donating ability (T. Ohwada et al., J. Org. Chem. 69 (2004) 7486), which take into account only properties of the initial base in question, but rather consider protonation reaction in its entirety. (doi: 10.5562/cca2121)

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Section: Resultsmentioning

confidence: 83%

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Radić¹,

Despotović²,

Vianello³

2012

Croat. Chem. Acta

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“…Thus, inspired by the earlier work of Gray and coworkers, [127] the required transformation was effected by treatment of bromide 129 with trimethylboroxine 130, [PdCl 2 -(dppf)] (10 mol %), and Cs 2 CO 3 in aqueous DMF at 100 8C, yielding compound 131 in 71 % yield. Crucially, not only was the presence of the vinylogous ester and the three unprotected hydroxy groups tolerated in this step, but also the delicate and highly strained "anti-Bredt" bridgehead olefin [128] emerged unscathed from the coupling reaction, underlining again the mildness of these protocols.…”

Section: The Suzuki Reactionmentioning

confidence: 99%

Palladium‐Catalyzed Cross‐Coupling Reactions in Total Synthesis

2005

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In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

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“…The that of 21e with the exception of the signal for C-6 which appeared at δ ϭ 15.26 as a low intensity triplet. 2,7 .0 4,6 ]heptane (21f): Compound 6 (1.08 g, 4.32 mmol) Photocyclization of 24c: Compound 24c (100 mg, 0.480 mmol) in ether (10 ml) was mixed at Ϫ78°C with tBuLi (5.40 ml, 8.64 was irradiated in 15 ml of ether with a mercury high-pressure lamp mmol). The pale yellow solution was stirred for 1 h at Ϫ78°C and at Ϫ12°C for 24 h in the presence of acetophenone (2.88 mg, 0.0240 charged with chlorotrimethylsilane (428 mg, 3.94 mmol).…”

Section: : Ir (Filmmentioning

confidence: 99%

“…After removal of the volatile products in vacuo, 23c (78.0 ture was allowed to warm to room temperature and hydrolyzed mg, 78%) was isolated as a colorless oil. 2,7 .0 4,6 ]heptane (23a): Compound 6 (1.30 g, 5.20 mmol) in ether (8.0 ml) was mixed at solvent removed in vacuo from a 0°C bath. According to NMR…”

Section: : Ir (Filmmentioning

confidence: 99%

“…Reaction of 6 with tBuLi (> 4 equiv.) gave rise to 1,6-dilithioLithium halide elimination has proved as an efficient method for the generation of strained olefins [2] and hydrocarbons [3] . This reaction has furnished evidence for the formation of 1,7-dehydroquadricyclane (1) [4] [5] , 1,5-dehydroquadricyclane (2) [6] and 1,2-dehydroquadricyclane (3) [7] , which could be trapped as Diels-Alder adducts.…”

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confidence: 99%

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Experiments Towards the Formation of 1,6-Dehydroquadricyclane and Density Functional Calculations on This and Related Molecules

Glück-Walther

Jarosch

Szeimies³

1998

Eur. J. Org. Chem.

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1,6‐Dibromoquadricyclane (6) was obtained from norbornadiene (11) by hydroboration, oxidation of the diol 12 to the diketone 14 and its conversion into 2,6‐dibromonorbornadiene (20) using tribromodioxaphosphole 16b followed by treatment of the mixture 17/18 with potassium tert‐butoxide in DMSO and photocyclization of 20. Reaction of 6 with tBuLi (2 equiv.) led to the formation of 1‐bromo‐6‐lithioquadricyclane 7, the NMR spectra of which were observed up to 0°C. 7 did not lose LiBr to give 4, but could be trapped with H2O and chlorotrimethylsilane to give 21e (53%) and 21f (64%). Reaction of 6 with tBuLi (> 4 equiv.) gave rise to 1,6‐dilithioquadricyclane (21c), whose NMR spectra could also be recorded. 21c was converted into the corresponding 1,6‐disubstituted quadricyclanes with D2O (87%), chlorotrimethylsilane (92%), dimethyl sulfate (55%), methyl chloroformate (45%), iodine monochloride (62%), and p‐toluenesulfonyl chloride (48%). − Density functional calculations using the B3LYP‐6‐31G* level of theory showed that 1,6‐dehydroquadricyclane (4) is a local energy minimum in its singlet electronic state. 4 contains a unique structure with 4 condensed cyclopropane units. The parent hydrocarbons 27 and 28, hitherto unknown, are also local energy minima in their singlet electronic states.

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Strained bridgehead double bonds

Cited by 166 publications

References 60 publications

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Palladium‐Catalyzed Cross‐Coupling Reactions in Total Synthesis

Experiments Towards the Formation of 1,6-Dehydroquadricyclane and Density Functional Calculations on This and Related Molecules

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