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Saccharide Libraries as Potential Templates for Regio- and Chiroselective Introduction of Two Functional Groups into
Tsutomu Ishi-I1, Kazuaki Nakashima, Seiji Shinkai
1Chemotransfiguration Project, Japan Science and Technology Corporation (JST), 2432 Aikawa, Kurume, Fukuoka 839-0861, Japan, and Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, 812-8581, Japan.
Abstract:
This paper reports regio- and chiroselective introduction of two boronic acid groups into [60]fullerene controlled by a saccharide used as a template molecule. The double [4+2] cycloadditions between [60]fullerene and 1:2 saccharide-boronic acid complexes 6-9 afforded [60]fullerene-bisadducts 12. Their structures were identified on the basis of (1)H and (13)C NMR, UV-vis, and CD spectroscopy, mass spectrometry, and chiral HPLC analysis. When 3-O-methyl-D-glucose (4) was used as the template molecule, high regioselectivity was achieved which gave trans-4 isomer 12a as a main isomer in 72.5% yield. The chiro- as well as regioselective preparation of e isomer 12c was attained in 81.4% ee from the 55.7% yield racemic mixture by the reaction using the D-mannitol-3,4-carbonate template (3). When the enantiomers, D-threitol (D-2) and L-threitol (L-2) were used as the templates, cis-3 isomers 12b and ent-12b with opposite chirality were yielded in 44.2 and 45.2% ee, respectively. On the other hand, 1-O-methyl-alpha-D-mannopyranoside template (5) featured nonselective cycloaddition.