The diastereoselectivity of electrophilic attack on trigonal carbon adjacent to a stereogenic centre: diastereoselective alkylation and protonation of open-chain enolates having a stereogenic centre carrying a silyl group at the ? position

Crump, R. A.; Fleming, Ian; Hill, John H.; Parker, David; Reddy, N. Laxma; Waterson, David

doi:10.1039/p19920003277

Cited by 71 publications

(31 citation statements)

References 54 publications

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“…27 At this point, the structure assignments of 42–45 were secure, although they are based on the known selectivity of the Kiyooka aldol reaction for the Si face with N -Ts-( S )-valine, which has been confirmed in numerous examples 23…”

Section: Resultsmentioning

confidence: 91%

Introduction of the (−)-Berkelic Acid Side Chain and Assignment of the C-22 Stereochemistry

Zhou²,

Snider³

2009

J. Org. Chem.

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A Kiyooka aldol condensation of an aldehyde with a trimethylsilyl ketene acetal and the oxazaborolidinone prepared from N-Ts-(S)-valine gives two of the four possible aldol adducts which were oxidized and deprotected to complete the synthesis of (−)-berkelic acid and (−)-22-epi-berkelic acid. This synthesis establishes the absolute stereochemistry and assigns the stereochemistry at C-22. A biosynthetic pathway is proposed that is consistent with the known absolute stereochemistry at the quaternary carbon of spiciferone A, spicifernin, and berkelic acid and provides a simple explanation for the differing stereochemistry at C-18 and C-19 of spicifernin and berkelic acid.

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Section: Resultsmentioning

confidence: 91%

Introduction of the (−)-Berkelic Acid Side Chain and Assignment of the C-22 Stereochemistry

Zhou²,

Snider³

2009

J. Org. Chem.

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“…Use of solid paraformaldehyde or addition of a preformed solution of formaldehyde in THF at -25°C to the enolate gave untrapped conjugate adduct along with some unidentified side products. [29] The high diastereoselectivity of conjugate addition could then arise from conformation 12, in which steric interactions between the tert-butyl group and the aryl substituent are minimised, and the full p-orbital of the carbanion is still reasonably well aligned with the S-O bond. The relative configurations of the centres α and β to the sulfinyl group were proven by X-ray crystallography of a derivative (see Figure 4).…”

Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis of Lignans of Three Structural Types from a Common Intermediate, Enantioselective Synthesis of (+)‐Yangambin

2014

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Enantioselective total synthesis of (+)‐yangambin was achieved. The key transformation is one‐pot conjugate addition/aldol reaction that involves an enantioenriched benzyl tert‐butyl sulfoxide, an enone, and gaseous formaldehyde to construct the bis(phenylpropanoid) backbone with excellent stereoselectivity and in good yield. Reduction of the ketone with diisobutylaluminium hydride and acid‐catalysed cyclisation in EtOH furnished (+)‐yangambin in good yield. The resulting synthesis is short, efficient and highly selective. Formation of 2,5‐diaryltetrahydrofuran lignans was observed as a side reaction in the final step of yangambin synthesis. Acid‐catalysed cyclisation of the aldol intermediate gave a completely different outcome. Dehydration to give an enone was followed by two electrophilic aromatic substitution reactions to furnish a derivative of the lignan lirionol.

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“…Following our earlier work, we added successively our phenyldimethylsilyl-cuprate reagent and a proton to the u,Punsaturated ester 5 to give the ester 6 with selectivity (91 :9) in favour of the syn relationship between the silyl and the methyl group, as usual in protonations of p-silyl enolates (Scheme 2). 4 We then reduced the ester group and protected the alcohol as its benzyl ether. The benzyl triflate method' was superior to the acid-catalysed method using benzyl trichloroacetimidate,6 because it avoided the easy formation of a cyclic acetal, and base-catalysed methods using benzyl halides give displacement of the phenyl group from the ~i l i c o n .…”

Section: Resultsmentioning

confidence: 99%

Stereocontrol of stereogenic centres para on a benzene ring using the SE2? reaction of a pentadienylsilane

Fleming¹,

Leslie²

1996

J. Chem. Soc., Perkin Trans. 1

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The diastereoselectivity of electrophilic attack on trigonal carbon adjacent to a stereogenic centre: diastereoselective alkylation and protonation of open-chain enolates having a stereogenic centre carrying a silyl group at the ? position

Cited by 71 publications

References 54 publications

Introduction of the (−)-Berkelic Acid Side Chain and Assignment of the C-22 Stereochemistry

Introduction of the (−)-Berkelic Acid Side Chain and Assignment of the C-22 Stereochemistry

Stereoselective Synthesis of Lignans of Three Structural Types from a Common Intermediate, Enantioselective Synthesis of (+)‐Yangambin

Stereocontrol of stereogenic centres para on a benzene ring using the SE2? reaction of a pentadienylsilane

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