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Organic Synthesis







Halonium Chemistry


            a. Catalytic Asymmetric Halocyclization

Our research group has recently reported the catalytic asymmetric chlorolactonization of alkenoic acids and unsaturated amides to furnish chiral heterocycles. These reactions are catalyzed by (DHQD)2PHAL in combination with various N-chlorinated hydantoins as the terminal chlorenium sources. Halofunctionalization of different compounds, understanding the mechanism of these transformations and the details of enantioselections are currently under investigation.




           b. Mechanistic Studies

Our research is also focused on dissecting the steps and revealing the mechanistic underpinnings of asymmetric halocyclizations. In collaboration with Professor Ned Jackson, we utilize both experimental results, such as kinetic analyses and thermodynamic meaurements, and theoretical calculations to derive at likely mechanisms provide insight into the origins of regio and enantio selection. These results are then parlayed into the next generation catalyst design.






Heterocyclic Methodologies

We are also interested in developing reactions that yields highly functionalized heterocyclic motifs in a robust way, with high regio and stereo control, from small and readily available families of molecules. Examples of such are the tandam aza-Payne hydroamination reaction to achieve highly decorated pyrrolidines or 3,4-dihydroxypyrrolidines the one-carbon homologative ring expansion relay chemistry, and the 1,2,n-triol cyclization, towards the preparation of a library of complex dihydropyrans.       



















Catalyst Design

Our venture in the field of asymmetric reactions have motivated us towards a simplistic approach in building small chiral motifs that can potentially trigger a variety of useful transformations with a high level of enantiocontrol.












Total Synthesis

Having all the tools to set up complexity in molecular structures, with high level enantio and stereo control, we are applying these methodologies towards the total synthesis of biologically interesting and synthetically challenging natural product motifs.








Recent Publications


  1. Ashtekar, K. D.; Ding, X.; Toma, E.; Sheng, W.; Gholami, H.; Rahn, C.; Reed, P.; Borhan, B. "Mechanistically Inspired Route toward Hexahydro-2H-chromenes via Consecutive [4+2] Cycloadditions", Org. Lett. 2016, 18(16), 3976-3979. [PDF]
  2. Ashtekar, K.D.; Vetticatt, M.; Yousefi, R.; Jackson, J. E.; Borhan, B. "Nucleophile-Assisted Alkene Activation: Olefins Alone are Often Incompetent, J. Am. Chem. Soc. 2016, 138(26), 8114-8119. [PDF]
  3. Soltanzadeh, B.; Jaganathan, A.; Staples, R. J; Borhan, B. "Highly Stereoselective Intermolecular Haloetherification and Haloesterification of Allyl Amide", Angew. Chem. Int. Ed. Engl. 2015, 54, 9517-9522. [PDF]
  4. Ashtekar, K. D.; Marzijarani Salehi, N.; Jaganathan, A.; Holmes, D.; Jackson, J. E.; Borhan, B. "A New Tool to Guide Halofunctionalization reactions: The Halenium Affinityu (HalA) Scale", J. Am. Chem. Soc. 2014, 136, 13355-13362. [PDF]
  5. Jaganathan, A.; Borhan, B. "Chlorosulfonamide Salts are Superior Electrophilic Chlorine Precursors for the Organocatalytic Asymmetric Chlorocyclization of Unsaturated Amides", Org. Lett 2014, 16(14), 3616-3619. [PDF]
  6. Yasamura, R.; Ashtekar, K. D.; Tonouchi, A.; Nehira, T.; Borhan, B.; Hashimoto, M. "7-beta- and 10-beta-Hydroxylated congeners of CAF-603; elucidation of absolute configuration of CAF-603 family, and their SAR studies in the anti-fungal activity", Tetrahedron 2013, 69(45), 9469-9474. [PDF]
  7. Yousefi, R.; Ashtekar, K. D.; Whitehead, D. C.; Jackson, J. E.; Borhan, B."Dissecting the Stereocontrol Elements of a Catalytic Asummetric Chlorolactonization: Syn Addition Obviates Bridging Chloronium", J. Am. Chem. Soc. 2013, 135, 14524-14527. [PDF]
  8. Jaganathan, A.; Staples, R. J.; Borhan, B. "Kinetic Resolution of Unsaturated Amides in a Chlorocyclization Reaction: Concomitant Enantiomer Differentiation and Face Selective Alkene Chlorination by a Single Catalyst", J. Am. Chem. Soc. 2013, 135, 14806-14813. [PDF]
  9. Garzan, A.; Jaganathan, A.; Salehi-Marzijarani, N.; Yousefi, R.; Whitehead, D. C.; Jackson, J. E.; Borhan, B. "Solvent-Dependent Enantiodivergence in the Chlorocyclization of Unsaturated Carbamates", Chem. Eur. J. 2013,19, 9015-9021. [PDF]
  10. Kulshrestha, A.; Salehi-Marzijarani, N,; Ashtekar, K. D.; Staples, R.; Borhan,B. " 3,4-Dihydroxypyrrolidines via Modified Tandem Aza-Payne/Hydroamination Pathway", Org. Lett. 2012, 14, 3592-3595. [PDF]
  11. Ashtekar, K. D.; Staples, R. J.; Borhan, B. "Development of a Formal Catalytic Asymmetric [4+2] Addition of Ethyl-2,3-butadienoate with Acyclic Enones",Org. Lett. 2011, 13, 5732-5735. [PDF]
  12. Kulshrestha, A.; Schomaker, J. M.; Holmes, D.; Staples, R. J.; Jackson, J. E.; Borhan, B. "Selectivity in the Addition Reactions of Organometallic Reagents to Aziridine-2-carboxaldehydes: The Effects of Protecting Groups and Substitution Patterns",Chem. Eur. J. 2011, 17(44), 12326-12339. [PDF]
  13. Hart, S. R.; Whitehead, D. C.; Travis, B.; Borhan, B. "Catalytic Oxidative Cleavage of Olefins Promoted by Osmium Tetroxide and Hydrogen Peroxide", Org. Biomol. Chem. 2011, 9, 4741-4744. [PDF]
  14. Whitehead, D. C.; Fhaner, M.; Borhan, B. "A Peptide Bromoiodinane Approach for Asymmetric Bromolactonization", Tet. Lett. 2011, 52, 2288-2291. [PDF]
  15. Jaganathan, A.; Garzan, A.; Whitehead, D. C.; Staples, R. J.; Borhan, B. "A Catalytic Asymmetric Chlorocyclization of Unsaturated Amides", Ang. Chem. Int. Ed. 2011, 50, 2593-2596. [PDF]
  16. Yousefi, R.; Whitehead, D. C.; Mueller, J. M.; Staples, R. J.; Borhan, B. "On the Chlorenium Source in the Asymmetric Chlorolactonization Reaction", Org. Lett. 2011, 13(4), 608-611. [PDF]
  17. Yan, J.; Garzan, A.; Narayan, R.; Vasileiou, C.; Borhan, B. "A minimalist approach for the structural revision of mucoxin", Chem. Eur. J. 2010, 16(46), 13749-13756. [PDF]