Enantioselective Synthesis
of Planar Chiral Paracyclophanes with Short ansa Chains
and Structure of Strained Dioxa[7]paracyclophane

Tatsuya Araki; Daiki Hojo; Keiichi Noguchi; Ken Tanaka

doi:10.1055/s-0030-1259539

LETTER

Enantioselective Synthesis of Planar Chiral Paracyclophanes with Short ansa Chains and Structure of Strained Dioxa[7]paracyclophane

Tatsuya Araki^a, Daiki Hojo^a, Keiichi Noguchi^b, Ken Tanaka*^a
^a Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
Fax: +81(42)3887037; e-Mail: tanaka-k@cc.tuat.ac.jp;
^b Instrumentation Analysis Center, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan

Abstract

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Abstract

The first enantioselective synthesis of planar chiral [7] and [8]paracyclophanes has been achieved by the cationic rhodium(I)-(S)-H₈-BINAP complex catalyzed [2+2+2] cycloaddition. Planar chiral [9]paracyclophanes were also synthesized by the same method. The first X-ray crystallographic analysis of the strained dioxa[7]paracyclophane revealed the significant deformation of the benzene ring from planarity.

Key words

alkynes - paracyclophanes - planar chirality - rhodium - [2+2+2] cycloaddition

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Referenzen

References and Notes

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Lowering the catalyst loading to 2 mol% resulted in poor conversion (at least <50%) of 1a and 2a under the same reaction conditions of Table [¹] .

Racemization of [9]paracyclophane 3ca was not observed at all in a DCE solution at 80 ˚C for 6 h.

The corresponding meta- and ortho-cyclophanes were also generated as minor byproducts.

Employing a more diluted reaction conditions (0.01-0.005 M) did not further improve the yield of 3aa.

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CCDC 801251 [(R)-(+)-3aa] contains the supplementary crystallographic data for this paper. This data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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Although the significant deformation of the benzene ring from planarity was observed in the strained [7]paracyclophane 3aa, the ^¹H NMR chemical shifts of the aromatic protons of 3aa appears in the standard aromatic region (δ = 8.28-7.56 ppm). Furthermore, isomerization of 3aa to the corresponding Dewar or prismane isomer was not observed in both solution and solid states at room temper-ature under visible light. These observations indicate that 3aa still possesses stable aromatic structure.

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