Salome Lopez

2‐ and 3‐Haloalkoxy Fischer Carbene Complexes of Chromium as Synthons for either Hydroxycyclopropanation or Oxaspirocyclopropanation of Alkenes

The thermal reaction of 2-haloethoxy- and 3-chloropropoxy(alkenyl)carbene complexes of chromium with electronically neutral alkenes furnished diastereoselectively the corresponding 1-haloalkoxy-l-vinylcyclopropanes that, subjected to subsequent halogen-lithium exchange reactions, provided vinylcyclopropanols or compounds containing the spiro[cyclopropane-tetrahydrofuran/tetrahydropyran] structure, depending on the nature of both the halogen atom and the lithiating reagent. The hydroxycyclopropanation reaction can be efficiently achieved in a one-pot fashion.

INTRAMOLECULAR REACTIONS OF ALKYNES WITH ALKENES CATALYZED BY PLATINUM AND GOLD

Two major pathways are followed in the reaction of alkenes with alkynes catalyzed by electrophilic transition metals. If the metal coordinates the alkyne and the alkene, an oxidative cyclometallation can ensue to give a metallacyclopentene, which usually evolves by β-hydrogen elimination (Alder-ene cycloisomerization). Alternatively, the selective coordination of the metal to the alkyne promotes an attack of the alkene (usually anti) to give cyclopropyl metal carbenes.