Synthesis of conformationally constrained 5-fluoro- and 5-hydroxymethanopyrrolidines. Ring-puckered mimics of gauche- and anti-3-fluoro- and 3-hydroxypyrrolidines

J Org Chem. 2011 May 20;76(10):3626-34. doi: 10.1021/jo200117p. Epub 2011 Apr 18.


N-acetylmethanopyrrolidine methyl ester and its four 5-syn/anti-fluoro and hydroxy derivatives have been synthesized from 2-azabicyclo[2.2.0]hex-5-ene, a 1,2-dihydropyridine photoproduct. These conformationally constrained mimics of idealized C(β)-gauche and C(β)-anti conformers of pyrrolidines were prepared in order to determine the inherent bridge bias and subsequent heteroatom substituent effects upon trans/cis amide preferences. The bridgehead position and also the presence of gauche(syn)/anti-5-fluoro or 5-hydroxy substituents have minimal influence upon the K(T/C) values of N-acetylamide conformers in both CDCl(3) (43-54% trans) and D(2)O (53-58% trans). O-Benzoylation enhances the trans amide preferences in CDCl(3) (65% for a syn-OBz, 61% for an anti-OBz) but has minimal effect in D(2)O. The synthetic methods developed for N-BOC-methanopyrrolidines should prove useful in the synthesis of more complex derivatives containing α-ester substituents. The K(T/C) results obtained in this study establish baseline amide preferences that will enable determination of contributions of α-ester substituents to trans-amide preferences in methanoprolines.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amides / chemistry
  • Molecular Conformation*
  • Proline / chemistry
  • Pyrrolidines / chemical synthesis*
  • Pyrrolidines / chemistry*
  • Stereoisomerism


  • Amides
  • Pyrrolidines
  • Proline