The Synthesis of Enantiopure ω‐Methanoprolines and ω‐Methanopipecolic Acids by a Novel Cyclopropanation Reaction: The “Flattering” of Proline

Conformationally constrained prolines (1,2) and pipecolic acids (3,4) can be synthesized stereoselectively by a novel cyclopropanation reaction. Considerable flattening of the ring can take place in the proline series. Such compounds for the preparation of peptidomimetics of therapeutic interest. Boc = tert-butoxycarbonyl.