8776
J. Am. Chem. Soc. 1999, 121, 8776-8782
Intramolecular C-H Insertion Reactions of Boroxy Fischer Carbene
Complexes. Regio- and Diastereoselective Modification of Terpenes
Jose´ Barluenga,*,† Fe´lix Rodr´ıguez,† Je´roˆme Vadecard,† Maximilian Bendix,†
Francisco J. Fan˜ana´s,† Fernando Lo´pez-Ortiz,‡, and Miguel A. Rodr´ıguez§,|
Contribution from the Instituto UniVersitario de Qu´ımica Organometa´lica “Enrique Moles”,
Unidad Asociada al C.S.I.C., UniVersidad de OViedo, Julia´n ClaVer´ıa, 8, E-33071 OViedo, Spain,
Departamento de Geometr´ıa, Topolog´ıa y Qu´ımica Orga´nica, Facultad de Ciencias Experimentales,
UniVersidad de Almer´ıa, E-04120 Almer´ıa, Spain, and Departamento de Qu´ımica,
UniVersidad de La Rioja, E-26071 Logron˜o, Spain
ReceiVed April 12, 1999
Abstract: In-situ-generated dialkylboroxy and diaminoboroxy Fischer carbene complexes lead to oxaborolane
or oxazaborolidine derivatives via an intramolecular C-H insertion reaction. Further oxidation of these
intermediates yields 1,3-diol or 1,2-amino alcohol derivatives. Diastereoselectivities as high as 99% are reached
when starting from boroxy Fischer carbene complexes derived from terpenes, which represents a regio- and
diastereoselective modification of this type of natural product. The influence of the Câ substituents relative to
the boron atom on the reaction path is studied, and a mechanism is proposed after identification of an intermediate
by NMR. In addition, theoretical calculations show the presence of a boron-metal interaction, which could
result as key step to the C-H insertion reaction.
Introduction
complexes offer the opportunity to modulate the carbene
reactivity by steric and electronic variation of the Lewis acidic
component. In particular, only a few examples of boroxy Fischer
carbene complexes have been described, and they were found
to decompose to a mixture of unidentified products upon
standing at room temperature.8 However, we have recently
reported new synthetic applications of this type of complexes.9
On the other hand, whereas some C-H insertion reactions are
known for cationic iron carbene complexes,10 only one example
that involves group 6 non-heteroatom-stabilized Fischer carbene
complexes has been reported.11 In addition, Wulff et al. propose
the formation of butanolide derivatives via a C-H insertion
Fischer-type alkoxy and aminocarbene complexes have
attracted much interest as useful synthons in organic and
organometallic synthesis.1 By contrast, the synthesis and
chemistry of bimetallic systems, in which the carbene hetero-
atom is bound to a second, electron-deficient metal2 (metal )
Si,3 Ti,4 Zr,5 Hf,6 and Th7), have been much less explored. Such
† Universidad de Oviedo.
‡ Universidad de Almer´ıa.
§ Universidad de La Rioja.
NMR studies.
| Theoretical calculations studies.
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10.1021/ja991161+ CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/10/1999