Theoretical predictions of torquoselectivity in pentadienyl cation electrocyclizations

Kallel, E. Adam; Houk, K. N.

doi:10.1021/jo00287a004

Cited by 57 publications

(38 citation statements)

References 2 publications

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“…[29] A survey of the literature concerning theoretical studies of the Nazarov reaction revealed some works aimed at the theoretical prediction of torquoselectivity in the electrocyclization process. However, these computational studies focused only on acyclic systems [34][35][36][37] and on the retro-Nazarov reaction. [38] In particular, the electronic [34] and stereoelectronic [35,36] effects exerted by b-substituents on simple pentadienyl cations were considered in the studies of Houk [34] and Smith [35,36] and their co-workers.…”

Section: Introductionmentioning

confidence: 99%

“…However, these computational studies focused only on acyclic systems [34][35][36][37] and on the retro-Nazarov reaction. [38] In particular, the electronic [34] and stereoelectronic [35,36] effects exerted by b-substituents on simple pentadienyl cations were considered in the studies of Houk [34] and Smith [35,36] and their co-workers. The recent increased interest in the Nazarov reaction involving cyclic systems, as well as the substantial lack of ab initio and density functional theory (DFT) calculations on the torquoselectivity of the Nazarov reaction involving cyclic substrates for which further complications arise from the conformational mobility of the ring in which one double bond is embedded, prompted us to embark on a quantum chemical study of the key step of the Nazarov reaction, namely the electrocyclization, depicted in Equations (1), (3), and (4).…”

Section: Introductionmentioning

confidence: 99%

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Density Functional Studies on the Nazarov Reaction Involving Cyclic Systems

Cavalli

Masetti

Recanatini

et al. 2006

Chemistry A European J

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Density functional theory (DFT) has been used to define the energy profiles of the Nazarov reaction involving cyclic systems. The calculations were carried out at the B3LYP/6-311G** level of theory and the solvent (dichloromethane) contribution was estimated by using the recently developed SM5.43R solvation model. DFT calculations were first carried out to determine the energy profiles associated with the electrocyclization reactions of 3-hydroxy- and 3-ethoxypentadienyl cations in which one of the double bonds is embedded in O-heterocyclic and carbocyclic systems. In particular, the effects on the reaction rate of modifications to the substrate, as well as the presence of the heteroatom in the cycle, have been investigated. The torquoselectivity of the electrocyclization reaction was then explored with substituted O-heterocycles to understand the factors that control the stereochemical outcome of the process that preferentially provides 2,5-trans-disubstituted products. These DFT-based results rationally explain most of the experimental observations related to the Nazarov reaction of the substrates herein investigated and could be useful in the rational interpretation, and likely in the prediction, of the outcome of Nazarov reactions involving other cyclic systems.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Density Functional Studies on the Nazarov Reaction Involving Cyclic Systems

Cavalli

Masetti

Recanatini

et al. 2006

Chemistry A European J

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“…[38] All these reactions have been well documented in the literature. The second set consists of three cations, the well-studied ring closure of the parent 4 e pentadienyl cation, [13,39,40,41] and its 3-hydroxy [42,43] and 1-aza derivatives [44] that received less attention, but that are of synthetic value for the preparation of cyclopentenones (Nazarov reaction) and pyrrole derivatives. The third group is composed of the 6 p-electron pentadienyl anion, [41,45] which does not cyclize, [46] and its 2-aza [47] and 2,4-diaza derivatives, which readily lead to the heterocyclic products.…”

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confidence: 99%

Improved Reaction and Activation Energies of [4+2] Cycloadditions, [3,3] Sigmatropic Rearrangements and Electrocyclizations with the Spin‐Component‐Scaled MP2 Method

Goumans

Ehlers

Lammertsma

et al. 2004

Chemistry A European J

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A new quantum mechanical scheme to calculate electronic correlation energies, spin-component-scaled MP2, was tested as a tool to predict reaction energies and barriers in computational organic chemistry. Three common pericyclic reactions with known unsatisfactory MP2 descriptions were reinvestigated with the modified MP2 approach, in which the parallel and anti-parallel spin components of the correlation energy are scaled separately. The SCS-MP2 calculated reaction and activation energies of nine Diels-Alder reactions, four [3,3] sigmatropic rearrangements, and ten electrocyclization reactions are compared to those of the MP2, B3 LYP, QCISD(T), and G3 methods. For each, the SCS-MP2 results are in excellent agreement with the experimental data and compare far more favorably to G3 than both MP2 and B3 LYP. Careful evaluation of the effect of the size of the atomic orbital (AO) basis set shows that the larger expansions improve the agreement with experiment for the SCS-MP2 method, while they get worse for both MP2 and B3 LYP.

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“…[33, 34a] The results for the process 34 3 35 agree with the latter in predicting a rather early transition state; E-35TS and Z-35TS show only 42 % of the total shortening of the distance between the termini. [34,35] The large energy of activation of 6 3 7 relative to 32u 3 33 is attributed to stabilization of the cationic centre of 6 by the electron-donating hydroxyl oxygen. The activation energies for 34 3 35 (3.15 kcal mol À1 34 3 Z-35 and 3.64 kcal mol À1 for 34 3 E-35) are similar to that reported for 32u 3 33 (5.0 kcal mol À1 ) [33] and, as for 32u 3 33, they are much lower than values calculated for the standard Nazarov cyclization 6 3 7 (18.89 kcal mol À1 according to DFT/6-31G* [33] calculations and 15.9 kcal mol À1 according to MP2/6-31G*).…”

Section: Resultsmentioning

confidence: 99%

“…It was then extracted with Et 2 O (3 Â 100 mL). 1 (7), 327 (20), 279 (12), 248 (23), 247 (75), 191 (100), 187 (21), 177 (24), 175 (29), 161 (36), 147 (34), 119 (36), 107 (26), 105 (41), 95 (28), 91 (47), 81 (24), 79 (28), 77 (23), 73 (62), 57 (47) -2-yl}-7-methylocta-2,7-dien-5-yn-4-ol (14 b): Following the general procedure for the preparation of propargyl alcohols, the reaction of alkyne 13 (1.0 g, 7.24 mmol) and crotonaldehyde 12 b (11) [M] , 233 (15), 192 (33), 191 (59), 147 (25), 133 (26), 119 (26) (21), 165 (34), 163 (13), 147 (16), 135 (28), 121 (22), 105 (17), 91 (22), 79 (14), 77 (20), 73 (42), 58 (100), 57 (33), 55 (15); HRMS for C 14 H 22 O 2 : calcd 222.1620; found 222.1618. The solution was stirred at this temperature for 30 min and at 0 8C for an additional 5 min before cooling down to À 78 8C, at which temperature benzoyl chloride (1.5 mL, 12.08 mmol) was added dropwise.…”

Section: Methodsmentioning

confidence: 99%

Torquoselectivity in the Cationic Cyclopentannelation of (2Z)-Hexa-2,4,5-trienal Acetals

et al. 2000

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Inter- and intramolecular trapping experiments and density functional theory ab initio calculations for model systems are consistent with the acid-catalyzed rearrangement of 2-[(1Z)-hexa-1,3,4-trienyl]dioxolanes 1 to tetrahydroalkylidenecyclopenta-1,4-dioxins 4; this involves the electrocyclic ring closure of substituted hydroxypentadienyl carbocations. The reaction, which may be considered a variant of the Nazarov cyclization, occurs much more readily than the standard Nazarov cyclization, proceeding rapidly even at -30 degrees C. B3LYP/6-31G**//HF/6-31G** calculations for models 36, 38 and 40 predict that the two alternative conrotations at the cyclization termini are associated with activation energies differing by 0.55, 0.56 and 1.60 kcalmol(-1), respectively, in favour of the R-outwards rotation. This last value corresponds to an E-41/Z-41 product ratio of >99:1 at -60 degrees C, in consonance with the experimental observation that divinylallene 1a rearranges exclusively to E-4a at temperatures below -30 degrees C. At higher temperatures the torquoselectivity of the reaction 1a-->4a is masked by subsequent isomerization to the Z isomer, the greater stability of which is attributable to steric interaction between the substituent at the exocyclic double bond and the bulky neighbouring tBu group in the E isomer.

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Theoretical predictions of torquoselectivity in pentadienyl cation electrocyclizations

Cited by 57 publications

References 2 publications

Density Functional Studies on the Nazarov Reaction Involving Cyclic Systems

Density Functional Studies on the Nazarov Reaction Involving Cyclic Systems

Improved Reaction and Activation Energies of [4+2] Cycloadditions, [3,3] Sigmatropic Rearrangements and Electrocyclizations with the Spin‐Component‐Scaled MP2 Method

Torquoselectivity in the Cationic Cyclopentannelation of (2Z)-Hexa-2,4,5-trienal Acetals

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