Directly observable carbonium ion-carbonium ion rearrangements.  I.  Kinetics and equilibria in the interconversion of trialkylcyclopentenyl cations

Sorensen, T. S.

doi:10.1021/ja00991a019

Cited by 41 publications

(39 citation statements)

References 26 publications

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“…However, ion 27 would rearrange n.m.r. spectra (in particular, the C-1 methyl group is a triplet and this has been shown in other cases (9) to be the result of coupling with a methylene group at C-4).…”

Section: Product Ionsmentioning

confidence: 84%

Kinetics of Pentadienyl Cation Cyclizations

Bladek¹,

Sorensen²

1972

Can. J. Chem.

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A series of methyl-substituted pentadienyl cations has been prepared and characterized. A careful study was then made of the rate at which these cations cyclize to give cyclopentenyl cation products. Rate constants and activation parameters have been determined for this rearrangement in several different solvents and at several different cation concentrations. There is an unexpectedly large factor of 10' difference in rate between the extremes of the cations studied and a rationalization of this is presented.The cyclopentenyl cation products themselves undergo numerous rearrangements involving methyl or hydride shifts and a detailed discussion of the tetramethyl case is given. It is shown that a 3-cyclopenten-I-yl cation intermediate is involved in these rearrangements.Une serie de pentadienylcations substitues par le methyle a ete preparee et caracterisee. Une etude soignee est faite sur la vitesse a laquelle ces cations se cyclisent pour donner les produits du cyclopentenylcation. Les constantes de vitesse et les parametres d'activation ont ett determines pour ce rearrangement dans une grande variete de solvants et pour diverses concentrations en cation. Un facteur inattendu de 10' a ett trouve dans la difference de vitesse entre les cations extr8mes ttudies; une rationalisation de ce fait est presentee.Les produits du cyclopentenylcation subissent eux-m8mes de nombreux rearrangements impliquant des dtplacements du mtthyle ou d'hydrure et une discussion detaillee du compose tetramethyl6 est donnee. On a montre que I'intermediaire cyclopenttne-3 yl-l cation est concerne dans ces rearrangements.

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Section: Product Ionsmentioning

confidence: 84%

Kinetics of Pentadienyl Cation Cyclizations

Bladek¹,

Sorensen²

1972

Can. J. Chem.

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“…(360 MHz): 7.05 (d, J = 19.0, 1 H, HvC(2)); 6.98 (d, J = 19.0, 1 H, H-C(I)); 6.77 (q, J = 6. 8,1 H,CloHl~OSi (182.37) Calc. C 65.87 H 9.95% Found C 65.82 H 9.73% (1 E,4E)-5-Phenyl-l-trirnethylsilyl-l, 4-pentadien-3-one (3h).…”

Section: (E/-l-methyl-l-rrimethylsilyl-l 4-pentadien-3-onementioning

confidence: 99%

Silicon‐Directed Nazarov Reactions II. Preparation and Cyclization of β‐Silyl‐substituted Divinyl Ketones

Jones¹,

Denmark²

1983

Helvetica Chimica Acta

109

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SummaryTwo general methods for the preparation of P-silyl-substituted divinyl ketones have been developed starting from either a, P-unsaturated aldehydes or simple ketones. Anhydrous FeC1, induces the cyclization to cyclopentenones under mild conditions and in good yields with predictable and complete control over the position of the double bond i n the five-membered ring. The observed effects of substituents on rate can be explained by a rate-determining cationic electrocyclization. Silyl substitution has been shown to retard the reaction.Introduction. -The incorporation into organic synthesis of reagents and methods based on organosilicon chemistry has been an area of enormous activity over the last 10-15 years [l]. The ability of silicon (suitably placed) to stabilize organic reactive intermediates has been put to good use to develop solutions to difficult or low yielding transformations. Of the two most important properties (stabilization of a-anions and 8-cations) it is the latter, commonly termed the 8-effect, [2] which has dominated the application of organosilicon-based methodology in synthesis [3]. As part of a program on the use of Si to control and direct electrocyclic reactions of cations [4] we selected, as point of entry, the well-known Nazarov cyclization [5] [40] (Scheme I).

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“…The formation of cyclopentenyl cations from pentadienyl cations were well documented . Compound 3 involved the establishment of intermediaries γ‐lactones 5 via a cyclopentenyl zwitterion, and one of these, 5c could be isolated (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

Novel π_2s+π_2a Electrocyclization of Triethylenic‐Malonic Acids Exemplified for a One‐Pot Synthesis of New γ‐Dilactones cis‐Fused with a Cyclopentene

Dillenschneider

Dufossé²,

Fouillaud³

et al. 2015

Journal of Heterocyclic Chem

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A new, easy and rapid synthesis of γ-dilactones is cis-fused with a cyclopentenic ring via cyclization of 7-chlorotriethylenic-malonic acids. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π 2s + π 2a conrotatory process. This cyclopentenyl cation led to unstable γ-lactones intermediates that are rearrange to more stable isomers. δ-lactones (6Z and 6E-(3-chlorobut-2-en-2-yl)-5-methyl-3,6-dihydro-2H-pyran-2-one) were obtained as secondary products. Mechanistic pathways were considered. The structures of the newly synthesized compounds were established by elemental and spectral data.

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Directly observable carbonium ion-carbonium ion rearrangements. I. Kinetics and equilibria in the interconversion of trialkylcyclopentenyl cations

Cited by 41 publications

References 26 publications

Kinetics of Pentadienyl Cation Cyclizations

Kinetics of Pentadienyl Cation Cyclizations

Silicon‐Directed Nazarov Reactions II. Preparation and Cyclization of β‐Silyl‐substituted Divinyl Ketones

Novel π_2s+π_2a Electrocyclization of Triethylenic‐Malonic Acids Exemplified for a One‐Pot Synthesis of New γ‐Dilactones cis‐Fused with a Cyclopentene

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Directly observable carbonium ion-carbonium ion rearrangements. I. Kinetics and equilibria in the interconversion of trialkylcyclopentenyl cations

Cited by 41 publications

References 26 publications

Kinetics of Pentadienyl Cation Cyclizations

Kinetics of Pentadienyl Cation Cyclizations

Silicon‐Directed Nazarov Reactions II. Preparation and Cyclization of β‐Silyl‐substituted Divinyl Ketones

Novel π2s+π2a Electrocyclization of Triethylenic‐Malonic Acids Exemplified for a One‐Pot Synthesis of New γ‐Dilactones cis‐Fused with a Cyclopentene

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Novel π_2s+π_2a Electrocyclization of Triethylenic‐Malonic Acids Exemplified for a One‐Pot Synthesis of New γ‐Dilactones cis‐Fused with a Cyclopentene