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Scheme 5 Total synthesis of PDE-II (2).
In summary, we have accomplished a highly efficient
method for the total synthesis of PDE-II (2) utilizing
one-pot copper-mediated intramolecular double amination.
The methodology enabled us to synthesize PDE-II (2) in
7.5% yield over 11 steps from tetrahydroisoquinoline 7.
Because of the high utility of the aryl amination reaction,5b,d,7,8
we believe that the synthetic strategy should be generally
applicable to a wide variety of nitrogen-containing heterocycles.
This work was financially supported by the Ministry of
Education, Culture, Sports, Science, and Technology, Japan,
the KAKENHI, a Grant-in-Aid for Scientific Research (B)
(20390003), Tohoku University Global COE program
‘International Center of Research and Education for Molecular
Complex Chemistry’, Kato Memorial Bioscience Foundation.
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10 Preparation of ketene silyl acetal 10 was carried out according to
Corey’s internal quench method: E. J. Corey and A. W. Gross,
Tetrahedron Lett., 1984, 25, 495. Additional TBAF was found to
be necessary for smooth removal of a trimethylsilyl group on
nitrogen.
Notes and references
11 Compound 11 was isolated as a mixture of diastereomers. The
relative stereochemistry was not determined due to the presence of
the rotamers.
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ꢁc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 2641–2643 | 2643