Nonplanar cyclobutane. Evidence for a conformationally controlled, classic mechanism in the deamination of cis- and trans-3-isopropylcyclobutylamine

Lillien, Irving; Doughty, R. A.

doi:10.1021/jo01274a033

Cited by 11 publications

(3 citation statements)

References 2 publications

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“…The suggestion was previously made that products may arise directly from the cyclobutyldiazonium ion. 21 However, it now appears more likely that the common precursor is the 2-alkylcyclopropylcarbinyl cation or ion pair formed by initial rate-determining rearrangement of the cyclobutyldiazonium ion. A concerted, suprafacial overlap pathway from ¿rans-diazonium intermediate 9 or 11 to /rans-cyclopropylcarbinyl cation 10 (large arrows) subsequent to disrotatory C-2-C-3 bond opening23 (small arrows) appears facile for both R = CHa and R = ¿-C3H7, since the transition state involves a net reduction in nonbonded interactions.…”

Section: Resultsmentioning

confidence: 99%

Nonplanar cyclobutane. Steric product control in the deamination of cis- and trans-3-methylcyclobutylamine

Lillien¹,

Handloser²

1969

J. Org. Chem.

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Section: Resultsmentioning

confidence: 99%

Nonplanar cyclobutane. Steric product control in the deamination of cis- and trans-3-methylcyclobutylamine

Lillien¹,

Handloser²

1969

J. Org. Chem.

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“…Cyclopropylcarbinyl (CPC) and bicyclobutonium (BCB) cations (C 4 H 7 + ) have been of great scientific interest since Roberts’ 1951 report that cyclobutyl and cyclopropylcarbinyl electrophiles solvolyze quickly to the same mixture of cyclobutyl, cyclopropylcarbinyl, and homoallyl products, hinting at a common, stabilized intermediate . After many years of scientific debate, the C 4 H 7 + intermediates are now understood as a mixture of triply degenerate σπ-bisected cyclopropylcarbinyl (CPC) I and nonclassical bicyclobutonium (BCB) II cations (Figure A), − the latter being the more stable structure (by 1.8 kcal/mol from MP2 calculations). − Solvolysis experiments of substituted cyclobutyl or cyclopropylcarbinyl electrophiles provide complex product mixtures in which the major component seems difficult to predict, even for simple substitution patterns (Figure B). − Nevertheless, over the years multiple synthetic approaches have reported CPC/BCB and cyclobutyl (CB) cations as intermediates toward cyclopropylcarbinyl, − cyclobutyl, , and homoallyl (HA) products. ,, Such cations have also been proposed as intermediates in the biosynthesis of various terpenes, using Density Functional Theory (DFT) calculations as support. − …”

Section: Introductionmentioning

confidence: 99%

Substituent Effects on the Equilibria between Cyclopropylcarbinyl, Bicyclobutonium, Homoallyl, and Cyclobutyl Cations

Larmore,

Champagne

2024

J. Org. Chem.

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The cyclopropylcarbinyl (CPC) and bicyclobutonium (BCB) structures of the C 4 H 7 + cation have been proposed as intermediates in various reactions forming cyclopropylcarbinyl, cyclobutyl, or homoallyl products. While these cations can react with nucleophiles stereospecifically, in each system there are usually multiple BCB/CPC cations in equilibrium with related cyclobutyl (CB) and homoallyl (HA) cations, from which stereospecificity is jeopardized. Using density functional theory (DFT) and DLPNO−CCSD(T) calculations, we studied the electronic and steric effects on the equilibria between mono-and polysubstituted C 4 H 7 + cations. We find that the shapes of the potential energy surfaces (PESs) vary significantly, with structures that are minima for a given substituent becoming high-energy transition structures for another. Electron-donating groups at C1, C2, or C3/C4 positions favor CPC, BCB/CB, and HA structures, respectively. Electron-withdrawing groups yield shallower PESs where multiple related structures are energetically accessible. Strong Hammett correlations (σ + ) are observed for the substituent effects, which appear to be additive. In addition, BCB cations with more substituents are energetically destabilized compared to CPC cations, except with donating substituents at the C2 position. This work allows predictions of the major structures expected in mixtures of CPC/BCB/ CB/HA cations for given substituent patterns, and of the major products produced from such cations.

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“…[5][6][7] Solvolysis experiments of substituted cyclobutyl or cyclopropylcarbinyl electrophiles provided complex product mixtures in which the major component seems unpredictable, even for simple substitution patterns (Figure 1B). [8][9][10][11][12][13][14][15][16][17][18][19][20] Nevertheless, over the years multiple synthetic approaches have reported CPC/BCB and cyclobutyl (CB) cations as intermediates toward cyclopropylcarbinyl, [21][22][23][24][25] cyclobutyl, 26,27 and homoallyl (HA) products. 22,28,29 Such cations have also been proposed as intermediates in the biosynthesis of various terpenes, using DFT calculations as support.…”

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confidence: 99%

Substituent effects on the equilibria between cyclopropylcarbinyl, bicyclobutonium, homoallyl, and cyclobutyl cations

Larmore,

Champagne

2023

Preprint

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The cyclopropylcarbinyl (CPC) and bicyclobutonium (BCB) structures of the C4H7+ cation have been proposed as intermediates in various synthetic transformations forming cyclopropylcarbinyl, cyclobutyl, or homoallyl products. It has recently been recognized that such cations, when generated from chiral electrophiles, are themselves chiral and can react with nucleophiles stereospecifically. However, the CPC and BCB cations are in equilibrium with each other and with other related structures such as the cyclobutyl (CB) and homoallyl (HA) cations, from which stereospecificity is not guaranteed. Currently, the effect of substitution on the composition of cation mixtures containing CPC/BCB/CB/HA cations is not understood, precluding the prediction and control of the major products generated from such cations. Using Density Functional Theory and DLPNO-CCSD(T) calculations, we have studied the electronic and steric effects on the equilibria between mono- and polysubstituted C4H7+ cations. Our results indicate that electron-donating groups at the C1 position favor CPC structures, while BCB/CB structures are favored for the C2 position and HA structures for the C3/C4 positions. Electron-withdrawing groups yield shallower potential energy surfaces where many related structures are energetically accessible. Strong Hammett correlations (σ+) are observed for the various substituent effects, which appear to be additive in nature. In addition, BCB cations with more substituents are energetically destabilized compared to CPC cations, except with donating substituents at the C2 position. This work provides a predictive model for the major structures observed in mixtures of CPC/BCB/CB/HA cations, for given substituent patterns.

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Nonplanar cyclobutane. Evidence for a conformationally controlled, classic mechanism in the deamination of cis- and trans-3-isopropylcyclobutylamine

Cited by 11 publications

References 2 publications

Nonplanar cyclobutane. Steric product control in the deamination of cis- and trans-3-methylcyclobutylamine

Nonplanar cyclobutane. Steric product control in the deamination of cis- and trans-3-methylcyclobutylamine

Substituent Effects on the Equilibria between Cyclopropylcarbinyl, Bicyclobutonium, Homoallyl, and Cyclobutyl Cations

Substituent effects on the equilibria between cyclopropylcarbinyl, bicyclobutonium, homoallyl, and cyclobutyl cations

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