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Synthesis 2018; 50(05): 1053-1089
DOI: 10.1055/s-0036-1589147
paper
© Georg Thieme Verlag Stuttgart · New York

Cobalt-Mediated [2+2+2] Cycloadditions of Alkynes to Benzo­-[b]furans and Benzo[b]thiophenes: A Potential Route toward Morphanoids

Tobias Aechtner
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
David A. Barry
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Ellen David
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Cédric Ghellamallah
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Daniel F. Harvey
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Alix de la Houpliere
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Monika Knopp
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Michael J. Malaska
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Dolores Pérez
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Kaspar A. Schärer
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Brian A. Siesel
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
K. Peter C. Vollhardt  *
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
,
Robert Zitterbart
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA   Email: kpcv@berkeley.edu
› Author AffiliationsSupport by the NIH (GM 22479) and NSF (CHE 0907800) is gratefully acknowledged.
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Publication History

Received: 12 October 2017

Accepted after revision: 14 November 2017

Publication Date:
21 December 2017 (online)

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Abstract

Exploratory studies of the CpCo-mediated [2+2+2] cycloaddition of alkynes to the 2,3-double bond of benzo[b]furans (and some benzo[b]thiophenes) are presented, with the general aim to access morphinan substructures. The basic feasibility of constructing Co-complexed tetrahydrophenanthro[4,5-bcd]furans (and -thiophenes) in moderate to good yields is demonstrated, with complete to extensive diastereoselectivity. Limitations are the apparent necessity for bulky (silylated) monoalkynes, the lack of regioselectivity in the cocyclization with unsymmetrical alkynes, and the sensitivity of the ligands, both complexed and uncomplexed, with respect to ring opening and rearrangement.

Key words

alkynes - benzofurans - cobalt - cycloaddition - morphine

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/s-0036-1589147.
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