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.