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Draft:Fu's Planar DMAP

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Chirality can be broken into four categories, central, axial, helical and planar.[1][2][3][4][5][6] Prof. Greg Fu's DMAP complex [C1], analogous to ferrocene, displays planar chirality and has shown broad application in asymmetric catalysis (Fig. 1a).[7][8] Fu first reported the synthesis of planar DMAP complex [C1] in 1998 (Fig. 1c).[9]  Synthesis was accomplished using a six-step route starting with para-nitration of commercially available 2,3-cyclopentenopyridine N-oxide. This was followed by sequential chlorination, dimethylamine SNAr, and acetylation using a Boekelheide reaction.[10] Sequential alcohol elimination, benzylic deprotonation and treatment with Iron (II) chloride and then pentaphenyl cyclopentadiene afforded racemic complex [C1]. Enantiomers were separated using chiral HPLC and X-Ray diffraction was used to characterize complex [C1] as an Iron 2+, d6, six coordinate 18 electron complex.[9][11]

Figure 1) a) Types of Chirality,[3] b) Fu's planar DMAP X-Ray crystal structure,[11] c) Synthesis of Fu's planar DMAP[9]

Mechanism

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Studies indicate the application of Fu's planar DMAP complex in catalysis can enable the control of enantioselectivity by two mechanistic pathways (Fig. 2). Planar DMAP can act as a Brønsted base enabling deprotonation of protic nucleophiles forming planar Brønsted acid-base ion pair complexes (pathway A).[12] These have been demonstrated to engage in enantioselective addition to electrophiles such as carbonyls.[12] Alternatively nucleophilic addition of planar DMAP to electrophiles can enable the generation of planar DMAP-electrophile complexes which can engage in enantioselective substitution (pathway B).[9]

Figure 2) Mechanistic Pathway A) planar Brønstead acid-base ion pair complex,[12] Pathway B) planar DMAP-electrophile complex[9]

Application in Asymmetric Catalysis

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Planar DMAP complexes (Fig. 3) have shown broad utility in asymmetric catalysis covering various reaction classes including desymmetrizations (Fig. 3a-c),[9][13][14] nucleophilic additions (Fig. 3d-e),[15][16][17][12] and annulation reactions (Fig. 4).[18][19][20] Treatment of racemic alcohols (Fig. 3a) and amines (Fig. 3b) with acylating reagents alongside complexes [C1] and [C3] has enabled preferential acylation of a single enantiomers.[13][14] This enabled separation of alcohols and amines using a kinetic resolution type strategy. Studies indicate these reactions proceed mechanistically via nucleophilic planar DMAP catalysis (pathway B) with planar DMAP attacking acylating reagents.[13][14] Application of this technique to meso alcohols (Fig. 3d) via the same mechanism (pathway B) has also enabled preferential enantiomer acetylation and separation via a kinetic resolution approach.[9]

Figure 3) a) alcohol acetylation,[13] b) amine acylation,[14] c) meso diol acetylation,[9] d) asymmetric nucleophilic addition,[15][16][17][12] e) asymmetric nucleophilic addition and curtius rearrangement,[12] f) catalysts

Application of [C1] has also enabled the asymmetric addition of various nitrogen and oxygen centered nucleophiles to ketenes including azoles, phenols, and enolates.[15][16][17] In the case of pyrrole and phenol nucleophiles, mechanistic studies suggest the planar DMAP catalysts engage in planar Brønsted acid-base catalysis (pathway A).[15] Mechanistic studies are yet to determine if enolate nucleophilic attack proceeds by pathways A or B.[16] Modification of this system has also enabled the asymmetric nucleophilic addition of hydrazoic acid to ketenes followed by Curtius rearrangement to the corresponding carbamates. Mechanistic studies indicate this transformation proceeds via planar Brønsted acid-base catalysis pathway A.[12]

Figure 4) a) b-lactone synthesis,[18] b) b-lactam staudinger synthesis,[19] c) [3+2] annulation,[20][21] d) catalyst

Treatment of ketenes with aldehydes and tosyl protected imines using complex [C1] (Fig. 4a-b) has enabled the asymmetric generation of lactones and lactams. Mechanistic studies indicate these may proceed via nucleophilic planar DMAP catalysis (pathway B)[18][19] The coupling of a,b-unsaturated acyl fluorides in [3+2] cycloadditions (Fig. 4c) has been proven to proceed via a nucleophilic catalytic pathway.[20] X-Ray crystallography studies enabled the isolation and characterization of reactive intermediates. This suggested the reaction proceeds via nucleophilic attack of planar DMAP to the acyl fluoride with concomitant allyl silane deprotecting, resulting in a facially selective [3+2] cycloaddition affording cyclopentones.[20][21]

References

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  1. ^ Jacobsen, Eric N.; Pfaltz, Andreas; Yamamoto, Hisashi (2003-09-22). Comprehensive Asymmetric Catalysis: Supplement 1. Springer Science & Business Media. ISBN 978-3-540-00333-5.
  2. ^ Noyori, R. (1989-01-01). "Centenary Lecture. Chemical multiplication of chirality: science and applications". Chemical Society Reviews. 18: 187–208. doi:10.1039/CS9891800187. ISSN 1460-4744.
  3. ^ a b Tang, Mengyao; Yang, Xiaoyu (2023). "Catalytic Enantioselective Synthesis of Inherently Chiral Molecules: Recent Advances". European Journal of Organic Chemistry. 26 (42): e202300738. doi:10.1002/ejoc.202300738. ISSN 1099-0690.
  4. ^ Wencel-Delord, J.; Panossian, A.; Leroux, F. R.; Colobert, F. (2015-05-26). "Recent advances and new concepts for the synthesis of axially stereoenriched biaryls". Chemical Society Reviews. 44 (11): 3418–3430. doi:10.1039/C5CS00012B. ISSN 1460-4744. PMID 25904287.
  5. ^ Liu, Wei; Qin, Tianren; Xie, Wansen; Yang, Xiaoyu (2022). "Catalytic Enantioselective Synthesis of Helicenes". Chemistry – A European Journal. 28 (68): e202202369. doi:10.1002/chem.202202369. ISSN 1521-3765. PMID 36063162.
  6. ^ Felder, Simon; Wu, Shiqi; Brom, Jules; Micouin, Laurent; Benedetti, Erica (2021). "Enantiopure planar chiral [2.2]paracyclophanes: Synthesis and applications in asymmetric organocatalysis". Chirality. 33 (9): 506–527. doi:10.1002/chir.23335. ISSN 1520-636X. PMID 34302702.
  7. ^ Fu, Gregory C. (2004-08-01). "Asymmetric Catalysis with "Planar-Chiral" Derivatives of 4-(Dimethylamino)pyridine". Accounts of Chemical Research. 37 (8): 542–547. doi:10.1021/ar030051b. ISSN 0001-4842. PMID 15311953.
  8. ^ Werner, Helmut (2012). "At Least 60 Years of Ferrocene: The Discovery and Rediscovery of the Sandwich Complexes". Angewandte Chemie International Edition. 51 (25): 6052–6058. doi:10.1002/anie.201201598. ISSN 1521-3773. PMID 22573490.
  9. ^ a b c d e f g h Ruble, J. Craig; Tweddell, Jennifer; Fu, Gregory C. (1998-05-01). "Kinetic Resolution of Arylalkylcarbinols Catalyzed by a Planar-Chiral Derivative of DMAP: A New Benchmark for Nonenzymatic Acylation". The Journal of Organic Chemistry. 63 (9): 2794–2795. doi:10.1021/jo980183w. ISSN 0022-3263.
  10. ^ Boekelheide, V.; Linn, W. J. (1954-03-01). "Rearrangements of N-Oxides. A Novel Synthesis of Pyridyl Carbinols and Aldehydes". Journal of the American Chemical Society. 76 (5): 1286–1291. Bibcode:1954JAChS..76.1286B. doi:10.1021/ja01634a026. ISSN 0002-7863.
  11. ^ a b Tao, Beata; Ruble, J. Craig; Hoic, Diego A.; Fu, Gregory C. (1999-06-01). "Nonenzymatic Kinetic Resolution of Propargylic Alcohols by a Planar−Chiral DMAP Derivative: Crystallographic Characterization of the Acylated Catalyst". Journal of the American Chemical Society. 121 (21): 5091–5092. Bibcode:1999JAChS.121.5091T. doi:10.1021/ja9906958. ISSN 0002-7863.
  12. ^ a b c d e f g Dai, Xing; Nakai, Takashi; Romero, Jan A. C.; Fu, Gregory C. (2007). "Enantioselective Synthesis of Protected Amines by the Catalytic Asymmetric Addition of Hydrazoic Acid to Ketenes". Angewandte Chemie. 119 (23): 4445–4447. Bibcode:2007AngCh.119.4445D. doi:10.1002/ange.200700697. ISSN 1521-3757.
  13. ^ a b c d Ruble, J. Craig; Latham, Hallie A.; Fu, Gregory C. (1997-02-01). "Effective Kinetic Resolution of Secondary Alcohols with a Planar−Chiral Analogue of 4-(Dimethylamino)pyridine. Use of the Fe(C5Ph5) Group in Asymmetric Catalysis". Journal of the American Chemical Society. 119 (6): 1492–1493. Bibcode:1997JAChS.119.1492R. doi:10.1021/ja963835b. ISSN 0002-7863.
  14. ^ a b c d Arai, Shigeru; Bellemin-Laponnaz, Stéphane; Fu, Gregory C. (2001-01-05). "Kinetic Resolution of Amines by a Nonenzymatic Acylation Catalyst". Angewandte Chemie International Edition. 40 (1): 234–236. doi:10.1002/1521-3773(20010105)40:1<234::AID-ANIE234>3.0.CO;2-K.
  15. ^ a b c d Hodous, Brian L.; Fu, Gregory C. (2002-08-01). "Enantioselective Addition of Amines to Ketenes Catalyzed by a Planar-Chiral Derivative of PPY: Possible Intervention of Chiral Brønsted-Acid Catalysis". Journal of the American Chemical Society. 124 (34): 10006–10007. Bibcode:2002JAChS.12410006H. doi:10.1021/ja027466x. ISSN 0002-7863. PMID 12188662.
  16. ^ a b c d Schaefer, Carsten; Fu, Gregory C. (2005). "Catalytic Asymmetric Couplings of Ketenes with Aldehydes To Generate Enol Esters". Angewandte Chemie. 117 (29): 4682–4684. Bibcode:2005AngCh.117.4682S. doi:10.1002/ange.200501434. ISSN 1521-3757.
  17. ^ a b c Wiskur, Sheryl L.; Fu, Gregory C. (2005-05-01). "Catalytic Asymmetric Synthesis of Esters from Ketenes". Journal of the American Chemical Society. 127 (17): 6176–6177. Bibcode:2005JAChS.127.6176W. doi:10.1021/ja0506152. ISSN 0002-7863. PMID 15853315.
  18. ^ a b c Wilson, Jonathan E.; Fu, Gregory C. (2004). "Asymmetric Synthesis of Highly Substituted β-Lactones by Nucleophile-Catalyzed [2+2] Cycloadditions of Disubstituted Ketenes with Aldehydes". Angewandte Chemie International Edition. 43 (46): 6358–6360. doi:10.1002/anie.200460698. ISSN 1521-3773. PMID 15558690.
  19. ^ a b c Hodous, Brian L.; Fu, Gregory C. (2002-02-01). "Enantioselective Staudinger Synthesis of β-Lactams Catalyzed by a Planar-Chiral Nucleophile". Journal of the American Chemical Society. 124 (8): 1578–1579. Bibcode:2002JAChS.124.1578H. doi:10.1021/ja012427r. ISSN 0002-7863. PMID 11853423.
  20. ^ a b c d Bappert, Erhard; Müller, Peter; Fu, Gregory C. (2006-06-15). "Asymmetric [3 + 2] annulations catalyzed by a planar-chiral derivative of DMAP". Chemical Communications (24): 2604–2606. doi:10.1039/B603172B. ISSN 1364-548X. PMID 16779492.
  21. ^ a b Bappert, E.; Muller, P.; Fu, G.C. (2006), CCDC 294368: Experimental Crystal Structure Determination (CIF), Cambridge Crystallographic Data Centre, doi:10.5517/CC9W9R6, retrieved 2025-06-08
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