Beyond the Divinyl Ketone: Innovations in the Generation and Nazarov Cyclization of Pentadienyl Cation Intermediates

Spencer, William T.; Vaidya, Tulaza; Frontier, Alison J.

doi:10.1002/ejoc.201300134

Cited by 172 publications

(48 citation statements)

References 120 publications

(50 reference statements)

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“…[1][2][3][4][5][6][7][8][9] The Nazarov reaction is often catalyzed by a Brønsted-or Lewis acid; coordination of which generates the requisite oxyallyl cation 2, which undergoes a stereospecific 4π-electron-5-atom electrocyclization to generate the C-C bond. Electrocyclization reactions are powerful transformations in organic synthesis that have been exploited to construct new C-C and new C-N bonds in a stereospecific manner.…”

Section: Introductionmentioning

confidence: 99%

Assembly of functionalized carbocycles or N-heterocycles through a domino electrocyclization–[1,2] migration reaction sequence

Jana

Driver

2015

Org. Biomol. Chem.

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The development of processes that streamline the synthesis of complex, functionalized carbocycles and heterocycles remains a hotly pursued topic because their scaffolds are present in a range of bioactive molecules and electronic materials. Although the Nazarov reaction has emerged to be useful in the synthesis of carbocycles and heterocycles, using an electrocyclization to trigger a migration remains underdeveloped. By constructing several bonds in one operation, domino reaction sequences are particularly effective at improving the efficiency of synthesis. The use of transition metal catalysts has the potential to render these processes stereoselective. This review examines the use of electrocyclization-[1,2] migrations to construct molecules and is organized by the type of ring constructed and the order of the two steps in this process.

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Section: Introductionmentioning

confidence: 99%

Assembly of functionalized carbocycles or N-heterocycles through a domino electrocyclization–[1,2] migration reaction sequence

Jana

Driver

2015

Org. Biomol. Chem.

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“…[3] Polarization of the acyclic dienone precursor [4] accelerates the Nazarov cyclization. [5] We have previously disclosed the highly diastereoselective triflimide-catalyzed cyclization that converts dienone 1 into cyclopentenone 2 in 80 % yield [Eq. (1)].…”

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confidence: 99%

Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters

et al. 2014

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Abstract:The diastereoselective asymmetric synthesis of vicinal all-carbon-atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported.The catalytic asymmetric synthesis of vicinal, all-carbonatom quaternary stereocenters presents a difficult challenge for which only a small number of solutions, none of which are completely general, have been described to date.[1] The enantioselective version of the reaction that is shown in Equation (1) would constitute a new solution to this problem. None of the asymmetric Nazarov cyclizations that have been described thus far [2] form vicinal quaternary stereocenters. At best, vicinal quaternary and tertiary stereocenters could be generated. [3] Polarization of the acyclic dienone precursor [4] accelerates the Nazarov cyclization.[5] We have previously disclosed the highly diastereoselective triflimide-catalyzed cyclization that converts dienone 1 into cyclopentenone 2 in 80 % yield [Eq. (1)].[6] The stereochemistry of 2 reveals that a conrotatory process, which is required to conserve orbital symmetry, has occurred. The polarization of "push-pull" dienone 1 and the rapid termination process that is enabled through loss of the 2-(trimethylsilyl)ethoxymethyl (SEM) group contribute to the success of this cyclization, which results in the formation of vicinal all-carbon-atom quaternary stereocenters. Rapid termination is especially important in the case of Nazarov cyclizations that lead to sterically congested products as Wagner-Meerwein rearrangements of the intermediate cyclic cation, which would be driven by relief of steric compression, have to be suppressed.[7] Herein, we report the first catalytic asymmetric Nazarov cyclization of fully substituted dienones for the construction of vicinal all-carbon-atom stereocenters.We had confidence that an asymmetric version of the cyclization that is shown in Equation (1) could be developed through systematic variation of the enol ether and ester groups, which could serve as recognition elements for a catalyst. The process could be optimized through iterative changes in catalyst, solvent, and additive(s). As the enol ether moiety must depart as a stable cation following the cyclization, its choice does not restrict the structural types of cyclopentenones that might be accessed by this reaction.We chose the (R)-BINOL scaffold for our screen of chiral Brønsted acids.[8] The broad utility of this class of compounds for a variety of catalytic asymmetric reactions is related to the ease with which substituents at the C3 and C3' positions can be introduced to quickly assemble a library of catalysts. [9] Catalyst optimization is summarized in Table 1. The phenyl ester group in 3 strongly influenced the enantioselectivity of the reaction. The ethyl ester analo...

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“…[1] The enantioselective version of the reaction that is shown in Equation (1) would constitute a new solution to this problem. [5] We have previously disclosed the highly diastereoselective triflimide-catalyzed cyclization that converts dienone 1 into cyclopentenone 2 in 80 % yield [Eq. At best, vicinal quaternary and tertiary stereocenters could be generated.…”

mentioning

confidence: 99%

“…None of the asymmetric Nazarov cyclizations that have been described thus far [2] form vicinal quaternary stereocenters. [5] We have previously disclosed the highly diastereoselective triflimide-catalyzed cyclization that converts dienone 1 into cyclopentenone 2 in 80 % yield [Eq. [3] Polarization of the acyclic dienone precursor [4] accelerates the Nazarov cyclization.…”

mentioning

confidence: 99%

Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters

et al. 2014

View full text Add to dashboard Cite

The diastereoselective asymmetric synthesis of vicinal all-carbon-atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported.

show abstract

Beyond the Divinyl Ketone: Innovations in the Generation and Nazarov Cyclization of Pentadienyl Cation Intermediates

Cited by 172 publications

References 120 publications

Assembly of functionalized carbocycles or N-heterocycles through a domino electrocyclization–[1,2] migration reaction sequence

Assembly of functionalized carbocycles or N-heterocycles through a domino electrocyclization–[1,2] migration reaction sequence

Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters

Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters

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