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

2001; Wiley; Volume: 7; Issue: 21 Linguagem: Inglês

10.1002/1521-3765(20011105)7

1521-3765

José Barluenga, Salomé López, Andrés A. Trabanco, Josefa Flórez,

Coordination Chemistry and Organometallics

The oxaspirocyclopropanation and the one-pot hydroxycyclopropanation of simple alkenes have been accomplished by thermal treatment with 2- and 3-haloalkoxy(alkenyl)carbene complexes of chromium followed by halogen–lithium exchange reactions (see scheme). Depending on the nature of both the halogen atom and the lithiating reagent, the formation of either a radical or ionic intermediate is presumed to account for these results. The thermal reaction of 2-haloethoxy- and 3-chloropropoxy(alkenyl)carbene complexes of chromium with electronically neutral alkenes furnished diastereoselectively the corresponding 1-haloalkoxy-1-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. El tratamiento térmico de complejos 2-haloetoxi- o 3-cloropropoxi(alquenil)carbeno de cromo con alquenos electrónicamente neutros condujo a los correspondientes 1-haloalcoxi-1-vinilciclopropanos con alta diastereoselectividad. Cuando estos compuestos se sometieron a una posterior reacción de intercambio halógeno-litio se aislaron vinilciclopropanoles a partir de los derivados iodados y tert-butillitio, o compuestos que contienen la estructura espiro[ciclopropano-tetrahidrofurano/tetrahidropirano] a partir de los derivados clorados y litio en polvo o una disolución de litio-naftaleno. La reacción de hidroxiciclopropanación puede realizarse one-pot de forma más eficiente. Supporting information for this article (chart showing observed difference NOEs enhancements for compounds 2 and 9 and NOEs enhancements from 2D NOESY spectra for compounds 3 a,b, 4 a,b, 6, 7 b, 8 a,b, 10 and 14) is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2001/f3178_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.