Unexpected Steric Effects of “Remote” Alkyl Groups on the Rate of Conjugate Additions to Alkyl α,β-Ethylenic Sulfones, Sulfoxides, and Esters

Usera, Aimee; Posner, Gary H.

doi:10.1021/jo062155g

Cited by 11 publications

(4 citation statements)

References 17 publications

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“…The reaction is relatively insensitive to sterics; an ortho , ortho -dichloro derivative is competitive with its ortho , para -isomer, which would not be expected in the conjugate addition pathway (see Supporting Information). 26 Finally, the excellent enantioselectivity is best rationalized by a reversible, but stereochemically determining, 1,2-addition adjacent to the chiral triazolium to give the Claisen precursor. In contrast, a C–C bond forming conjugate addition would be an irreversible stereochemically determining step.…”

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confidence: 99%

An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes

et al. 2010

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In the presence of a chiral azolium salt (10 mol %), enols and ynals undergo a highly enantioselective annulation reaction to form enantiomerically enriched dihydropyranones via an N-heterocyclic carbene catalyzed variant of the Claisen rearrangement. Unlike other azolium-catalyzed reactions, this process requires no added base to generate the putative NHC-catalyst, and our investigations demonstrate that the counterion of the azolium salt plays a key role in the formation of the catalytically active species. Detailed kinetic studies eliminate a potential 1,4-addition as the mechanistic pathway; the observed rate law and activation parameters are consistent with a Claisen rearrangement as the rate-limiting step. This catalytic system was applied to the synthesis of enantioenriched kojic acid derivatives, a reaction of demonstrated synthetic utility for which other methods for catalytic enantioselective Claisen rearrangements have not provided a satisfactory solution.

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confidence: 99%

An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes

et al. 2010

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“…Although Cys thiol is a strong nucleophile in basic media, − it is usually employed on solid support as anchor site for moieties via disulfide formation . Alternatively, S N reactions have been reported for solid-support anchorage of mercaptans to chlorotrityl, , Wang’s bromo, and CPG resins .…”

Section: Resultsmentioning

confidence: 99%

Solid-Phase Synthesis of Chiral Bicyclic Guanidinium Oligomers

et al. 2009

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A simple solid-phase synthesis of thioether-linked chiral bicyclic guanidinium oligomers for cell internalization purposes has been developed. The approach is based on a Merrifield-like peptide synthesis on Rinkamide-p-methylbenzhydrylamine resin functionalized with Cys(methoxytrityl). A difunctionalized bicyclic guanidinium synthon, bearing both electrophile (O-mesyl) and protected nucleophile (S-methoxytrityl) group, is repeatedly grafted via a nucleophilic substitution. The sequence requires removal of methoxytrityl, reduction with 1,4-dithiothreitol to cleave any adventitious disulfides, coupling and capping with benzyl bromide. Moreover, Alloc protection of the alpha-amino group of the initial cysteine, provides a potential handle for cargo attachment after oligomer elongation to the desired internalizing agent and prior to cleaving it from the resin. Finally, a bicyclic guanidinium monomer containing an amino group and a carboxylic acid function has been evaluated as an alternative building block for novel amide-bridged oligomers or peptidomimetics.

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“…1 [18] DMF (66 μL, 0.85 mmol, 0.1 equiv.) was added to a solution of triethyl phosphonoacetate (2.68 mL, 13.5 mmol, 1.5 equiv.)…”

Section: Ethyl (E)-3-(4-methoxyphenyl)-2-propenoate (2f)mentioning

confidence: 99%

An Efficient Partial Reduction of α,β‐Unsaturated Esters Using DIBAL‐H in Flow

2014

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The partial reduction of α,β‐unsaturated esters and benzoate derivatives to form the corresponding aldehydes was achieved using a flow reactor system within 1 s at a high flow rate (18 mL min–1) under cryogenic conditions (–97 °C). Commercially available diisobutylaluminium hydride (DIBAL‐H) was used as the reductant. The desired enals and benzaldehyde derivatives, except for 4‐methoxycinnamate and 4‐methoxybenzoate, were formed selectively and redox economically in moderate to high yields.

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Unexpected Steric Effects of “Remote” Alkyl Groups on the Rate of Conjugate Additions to Alkyl α,β-Ethylenic Sulfones, Sulfoxides, and Esters

Cited by 11 publications

References 17 publications

An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes

An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes

Solid-Phase Synthesis of Chiral Bicyclic Guanidinium Oligomers

An Efficient Partial Reduction of α,β‐Unsaturated Esters Using DIBAL‐H in Flow

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