Diastereoselective Synthesis of <i>N</i>‐Substituted Planar Chiral Ferrocenes Using a Proline Hydantoin‐Derived Auxiliary

Metallinos, Costa; John, Joshni; Zaifman, Josh; Emberson, Kassandra

doi:10.1002/adsc.201100862

Cited by 34 publications

(24 citation statements)

References 48 publications

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“…50-60%). These results mirrored the behavior of syn-13 with bases other than t-BuLi [14] and suggested that the origin of stereoselectivity for both substrates was Cp ring-controlled.…”

Section: Resultssupporting

confidence: 78%

“…As anticipated based on the crystal structure for 16a, products ent-18a-c were enantiomers of the imidazolones derived previously from syn-13 (17a-c!18a-c), as measured by specific rotation and chiral stationary phase HPLC analysis. [14] It is clear from these results that the configuration of the silyloxy-containing b-ferrocenyl stereogenic center is the primary determinant of the sense of planar chiral induction in these substrates.…”

Section: Resultsmentioning

confidence: 94%

“…[14] Quench of the resulting carbanion with 2.5 equivalents of iodomethane, dimethyl disulfide or 1,2-diiodoethane gave the expected 2-substituted ferrocenes 16a-c (Scheme 2). All products appeared to be single diastereomers according to 1 H and 13 C NMR data.…”

Section: Resultsmentioning

confidence: 99%

“…Whereas syn-13 was produced stereoselectively by a one-pot stepwise hydrosilylation, [14] anti-13 was most easily obtained via isolation of a ca. 1:1 mixture of hemiaminals 15 after reduction with Schwartzs reagent (Scheme 1).…”

Section: Resultsmentioning

confidence: 99%

“…[14] Derived from l-proline hydantoin, the new directing group is unique in that it has b,g-stereogenic centers, but its lithiation diastereoselectivity is insensitive to the size of the base used for deprotonation (LDA, LiTMP, n-BuLi, i-PrLi or t-BuLi). [14] These observations implied that lithiation selectivity may be Cp ring-controlled in this case, as in Ugis system. If so, it was reasonable to ascribe a more important role for the proximal and relatively bulky bsilyloxy moiety than the g-stereocenter of the pyrrolidine ring in determining pro-S p versus pro-R p deprotonation.…”

Section: Introductionmentioning

confidence: 99%

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Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers

et al. 2013

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Diastereoselective induction of planar chirality in ferrocenes often employs chiral sulfur-, carbon-or phosphorus-based directing groups. The origin of stereoselectivity in these reactions may be classified as (a) cyclopentadiene (Cp) ring-controlled or (b) base-controlled. These two categories are represented by auxiliaries that typically have stereogenic centers a or g to the ferrocene core, respectively. In this study, it is shown that (À)-2-ferro-imidazol-3-one, the anti-epimer of the previously reported syn-(1R,7aS) substrate, induces lithiation of the pro-R p rather than the pro-S p Cp hydrogen in > 95:5 dr, leading to enantiomers of the syn-derived planar chiral imidazolones upon electrophile quench and elimination. This outcome provides a practical way to prepare planar chiral enantiomers in this series without having to synthesize a more expensive d-proline-derived starting material, since both the syn and anti starting materials are available from a common l-proline-derived intermediate. The origin of stereoselectivity in lithiation of the syn and anti epimers, which have b,g-stereogenic centers, appears to be driven primarily by the conformational bias exerted by the b-silyloxy moiety in each chiral auxiliary, which positions the urea carbonyl within the proximity of one of the two prochiral ortho Cp hydrogens. As such, stereoselectivity is likely Cp ring-controlled for both compounds despite their lack of a-ferrocenyl stereogenic centers. This conclusion is supported by the insensitivity of lithiation selectivity to the bulkiness of the base, comparisons of enantiomers, deuteration experiments, nOe difference studies, and computational modeling of the ground states and lithiation transition states for both substrates.

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“…50-60%). These results mirrored the behavior of syn-13 with bases other than t-BuLi [14] and suggested that the origin of stereoselectivity for both substrates was Cp ring-controlled.…”

Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers

et al. 2013

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Low Pressure Asymmetric Hydrogenation of Quinolines using an Annulated Planar Chiral N‐Ferrocenyl NHC‐Iridium Complex

John¹,

Wilson‐Konderka²,

Metallinos³

2015

Adv Synth Catal

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Annulated planar chiral N-ferrocenylimidazolones,o btainedb ya cid-mediated cyclization of diphenylmethanol derivatives,m ay be reduced with diisobutylaluminium hydide (DIBAL-H) to afford as eries of surprisingly stable and isolable hemiaminal ether aminals. Tw oo ft hese derivatives can be oxidized with triphenylcarbenium tetrafluoroborate to imidazolinium salt precursors of N-heterocyclic carbenes (NHCs). Deprotonation of these salts in the presenceo f( cyclooctadiene)iridium chloride dimer {[Ir(COD)Cl] 2 }p rovides chiral coordination complexes bearing N-ferrocenyl NHCsw ith unique rigid tetracyclic frameworks.C ationic analogues of these complexes catalyze the asymmetric hydrogenation of 2-substituted quinolines under very mild conditions( 1mol% complex, 1mol% PPh 3 ,1 -5 atm H 2 , toluene,2 5 8 8 C) in appreciable enantioselectivity (up to 90:10 er). Thes ensitivityo ft he hydrogenation process to changes in the phosphineadditive suggests that an outer-sphere reactionm echanism may be involved, as proposed for ar elated achiral NHC-Ir complexr eported by Crabtree and co-workers.

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Practical Access to Planar Chiral 1,2‐(α‐Ketotetramethylene)‐ ferrocene by Non‐Enzymatic Kinetic Resolution and Conclusive Confirmation of its Absolute Configuration

et al. 2015

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The asymmetric transfer hydrogenation (ATH) of racemic 1,2‐(α‐ketotetramethylene)ferrocene using the [N‐(tosyl)‐1,2‐diphenylethylendiamine]ruthenium(II) complex [TsDPEN‐Ru(II)] as catalyst takes place with a high level of kinetic resolution to deliver the ketone in up to 99% ee. The X‐ray crystallographic structure of a derivative of the alcohol co‐product serves to confirm conclusively both the absolute configuration of 1,2‐(α‐ketotetramethylene)ferrocene and the endo‐reduction selectivity.

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Diastereoselective Synthesis of N‐Substituted Planar Chiral Ferrocenes Using a Proline Hydantoin‐Derived Auxiliary

Cited by 34 publications

References 48 publications

Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers

Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers

Low Pressure Asymmetric Hydrogenation of Quinolines using an Annulated Planar Chiral N‐Ferrocenyl NHC‐Iridium Complex

Practical Access to Planar Chiral 1,2‐(α‐Ketotetramethylene)‐ ferrocene by Non‐Enzymatic Kinetic Resolution and Conclusive Confirmation of its Absolute Configuration

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