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Synfacts 2014; 10(9): 0926
DOI: 10.1055/s-0034-1378599
Synthesis of Materials and Unnatural Products
© Georg Thieme Verlag Stuttgart · New York

[2+2+2] to Twist: Synthesis of [9]- and [11]Helicene-Like Molecules

Contributor(s):
Timothy M. Swager
,
Kathleen R. White
Kimura Y, Fukawa N, Miyauchi Y, Noguchi K, Tanaka K * Tokyo Institute of Technology, Tokyo University of Agriculture and Technology, and Japan Science and Technology Agency, Saitama, Japan
Enantioselective Synthesis of [9]- and [11]Helicene-Like Molecules: Double Intramolecular [2+2+2] Cycloaddition.

Angew. Chem. Int. Ed. 2014;
53: 8480-8483
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Publication History

Publication Date:
18 August 2014 (online)

 
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Key words

helical structures - [2+2+2] cycloaddition - alkynes - enantioselectivity - rhodium

Significance

Higher order helicene-like molecules are difficult to synthesize enantioselectively due to steric constraints. The authors report the enantioselective synthesis of [9]- and [11]helicene-like molecules 4 and 6 via double intramolecular [2+2+2] cycloaddition of hexaynes, catalyzed by a cationic rhodium/chiral bis(phosphine) complex. Notably, molecules 4 and 6 both contain completely ortho-fused ring systems.


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Comment

The authors report that the second cycloaddition is difficult to achieve because it proceeds through the highly sterically encumbered intermediate 3. The diastereoselective synthesis of an [11]helicene-like molecule was reported previously (P. Sehnal et al. Proc. Natl. Acad. Sci. 2009, 106, 13169), but the reported molecule contained three para-fused rings.


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