The protonated cyclopropane route to bicyclic cations

Kirmse, Wolfgang; Streu, Joachim

doi:10.1021/jo00380a007

Cited by 9 publications

(3 citation statements)

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“…The HMBC correlations were observed between the hydrogens H-1, H-6, and H-19 and the carbon C-10 and between the hydrogens H-1, H-19, and H-6 and the carbon C-5 (Figure ). Further HMBC correlations observed between the hydrogens H-20, H-6, and H-12 and the carbon C-9 indicated that 2 had a bridged cyclic subunit, a tricyclo[3.2.1.0 2,7 ]octane system. Then, 2 was recrystallized from methanol, and the crystals were subjected to X-ray crystallographic analysis, which revealed the relative structure of 2 to be as shown in Figure .…”

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Salvileucalin B, A Novel Diterpenoid with an Unprecedented Rearranged Neoclerodane Skeleton from Salvia leucantha Cav.

et al. 2008

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Salvileucalin B (2), having an unprecedented rearranged neoclerodane skeleton, was isolated from the aerial parts of Salvia leucantha Cav. (Labiatae) along with salvileucalin A (1). The absolute structures were elucidated by spectroscopic analysis, X-ray crystallographic analysis, and vibrational circular dichroism. Compound 2 represents a novel neoclerodane, characterized by a tricyclo[3.2.1.0 (2,7)]octane substructure incorporating the exocyclic C-20 methylene of 1. This molecule exerted cytotoxic activity against A549 and HT-29 cells with IC50 values of 5.23 and 1.88 microg/mL, respectively.

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“…Salvileucalin B is the first natural product having a caged carbon framework, tricyclo[3.2.1.0 2,7 ]octane, among neoclerodane diterpenoids. A plausible biogenetic pathway is shown in Scheme .…”

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Salvileucalin B, A Novel Diterpenoid with an Unprecedented Rearranged Neoclerodane Skeleton from Salvia leucantha Cav.

et al. 2008

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“…This type of binding is consistent with the observations long reported for the interactions of a cyclopropane ring with an alpha carbon, and isotopic scrambling experiments show that such interchanges are rapid for a sec‐butyl cation. Indeed, there are numerous reports of rapid migrations involving three‐membered rings within cyclic systems, and the skeletal isomerization route we are proposing for PAO may simply be an extension of these transformations to intermediates that do not have a large ring system. The well‐known investigations of the 2‐norbornyl cation also demonstrate the stabilizing effects of corner‐protonated cyclopropyl species.…”

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Behavior of protonated cyclopropyl intermediates during polyalphaolefin synthesis: Mechanism and predicted product distribution

Gee

Small

Hope

2012

J of Physical Organic Chem

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A new mechanism for the origin of multiple skeletal isomers observed in the cationic dimerization of 1-decene is proposed, and products that should form based on this mechanism are predicted. A protonated cyclopropyl intermediate appeared to form directly from combination of 2-decyl carbocation with 1-decene; formation of this intermediate did not appear to occur via ring closure of a branched secondary carbocation. The authors propose that rapid, repeated isomerizations of the protonated cyclopropyl intermediates lead to multiple skeletal isomers in decene dimers. The proposed mechanism can account for structures previously identified in mixtures of decene dimers and butene dimers.

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Umlagerungen und Ringöffnung von 3‐ und 5‐Methylbicyclo[2.1.1]hex‐2‐yl‐Kationen

1987

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Synthesen und Konfigurationszuordnung3-Methylbicyclo[2.1.1]hexan-2-on (4) entsteht durch Photocycloaddition aus 4-Methyl-l,5-hexadien-3-on (3)9'. LiA1H4-Reduktion von 4 ergab die 3-Methylbicyclo-[2.l.l]hexan-2-ole 6 und 7 (72:28), die zwar analytisch (GC auf Kapillarsaulen), aber nicht praparativ getrennt werden konnten. Folgende Argumente ordnen 6 die cis-(lc1,2~,3a,4a)-Konliguration zu: 1) Bei kinetischer Reaktionslenkung ist aus sterischen Grunden die bevorzugte Bildung von 6 zu erwarten. 2) Das thermodynamisch stabilere Isomere sollte 7 sein. Tatsachlich kehrte sich bei Behandlung des Gemischs mit Aluminium-2-propanolat/2-Propanol/ Aceton das Verhaltnis 6:7 um (36:64). 3) Im 'H-NMRSpektrum von Bicyclo[2.l.l]hexan-2-01(2, X = OH) findet man die Kopplungskonstanten J2p,3p = 7.2 Hz (Dihedralwinkel ~0 ' ) und Jzpza = 2.0 Hz"). Nur 2-H von 6 zeigt eine Kopplung von 7 Hz, wahrend 2-H von 7 als breites Singulett erscheint. 4) Im Vergleich zu Bicyclo[2.1 .l]hexan-2-01 [6(2-H) = 4.411 ist 2-H von 7 (6 = 3.78) starker abgeschirmt als 2-H von 6 (6 = 4.24). 5) Zusatz von Eu(fod), verschiebt das 3-CH3-Signal von 6 weiter als das der 3-CH3-Gruppe von 7.Chem. Ber. 120, 1301 -1306 (1987)

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The protonated cyclopropane route to bicyclic cations

Cited by 9 publications

References 6 publications

Salvileucalin B, A Novel Diterpenoid with an Unprecedented Rearranged Neoclerodane Skeleton from Salvia leucantha Cav.

Salvileucalin B, A Novel Diterpenoid with an Unprecedented Rearranged Neoclerodane Skeleton from Salvia leucantha Cav.

Behavior of protonated cyclopropyl intermediates during polyalphaolefin synthesis: Mechanism and predicted product distribution

Umlagerungen und Ringöffnung von 3‐ und 5‐Methylbicyclo[2.1.1]hex‐2‐yl‐Kationen

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