Journal
TETRAHEDRON
Volume 68, Issue 5, Pages 1407-1416Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2011.12.031
Keywords
Enantioselective; ortho-Lithiation; Planar chirality; Paracyclophane
Categories
Funding
- Japan Society for the Promotion of Science
- Ministry of Education, Culture, Sports, Science and Technology, Japan [23655091]
- Grants-in-Aid for Scientific Research [23655091] Funding Source: KAKEN
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The asymmetric induction of planar chirality in 1,n-dioxa[n]paracyclophane derivatives via asymmetric ortho-lithiation is described. Enantioselective ortho-lithiation of unflippable 1,n-dioxa[n]paracyclophanes (n <= 11) using sec-BuLi-(-)-sparteine at -78 degrees C and subsequent treatment with electrophiles gave the corresponding planar-chiral monosubstituted paracyclophanes with excellent ee. Further lithiation of these compounds and treatment with electrophiles gave planar-chiral paracyclophanes with two different substituents. Dilithiation of unflippable 1,n-dioxa[n]paracyclophanes gave the corresponding C(2)symmetrical disubstituted products with almost perfect ee. In the case of flippable 1,n-dioxa[n]paracyclophanes (n >= 12), a stepwise reaction was required for the highly enantioselective formation of disubstituted products. (C) 2011 Elsevier Ltd. All rights reserved.
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