Titanocene-Catalyzed Cascade Cyclization of Epoxypolyprenes: Straightforward Synthesis of Terpenoids by Free-Radical Chemistry
José Justicia
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAntonio Rosales
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorElena Buñuel Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Search for more papers by this authorJuan L. Oller-López
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorMónica Valdivia
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAli Haïdour Dr.
Scientific Instrument Center, Granada, 18071, Spain
Search for more papers by this authorJ. Enrique Oltra Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAlejandro F. Barrero Prof. Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorDiego J. Cárdenas Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Search for more papers by this authorJuan M. Cuerva Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorJosé Justicia
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAntonio Rosales
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorElena Buñuel Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Search for more papers by this authorJuan L. Oller-López
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorMónica Valdivia
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAli Haïdour Dr.
Scientific Instrument Center, Granada, 18071, Spain
Search for more papers by this authorJ. Enrique Oltra Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorAlejandro F. Barrero Prof. Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorDiego J. Cárdenas Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Search for more papers by this authorJuan M. Cuerva Dr.
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Granada, 18071, Spain, Fax: (+34) 958-248-437
Search for more papers by this authorGraphical Abstract
The total synthesis of a wide range of complex terpenoid skeletons, including monocyclic, bicyclic, and tricyclic natural products, is facilitated by employing a novel reaction cascade based on the combination of biomimetic strategies with titanocene catalysis. For example, the titanocene-catalyzed radical cyclization of 2,3-oxidosqualene mainly gave malabaricatrienes (see scheme). Mechanistically the reaction presumably occurs via discrete carbon-centered radicals.
Abstract
The titanocene-catalyzed cascade cyclization of epoxypolyenes, which are easily prepared from commercially available polyprenoids, has proven to be a useful procedure for the synthesis of C10, C15, C20, and C30 terpenoids, including monocyclic, bicyclic, and tricyclic natural products. Both theoretical and experimental evidence suggests that this cyclization takes place in a nonconcerted fashion via discrete carbon-centered radicals. Nevertheless, the termination step of the process seems to be subjected to a kind of water-dependent control, which is unusual in free-radical chemistry. The catalytic cycle is based on the use of the novel combination Me3SiCl/2,4,6-collidine to regenerate the titanocene catalyst. In practice this procedure has several advantages: it takes place at room temperature under mild conditions compatible with different functional groups, uses inexpensive reagents, and its end step can easily be controlled to give exocyclic double bonds by simply excluding water from the medium.
Supporting Information
Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2004/f5647_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.
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