標題: | Regioselectivity in the 1,3-dipolar cycloaddition of adamantylidenefulvene and its modification by inclusion in cyclodextrins' solutions |
作者: | Chu, Jean-Ho Li, Wan-Sheung Chao, Ito Lee, Gene-Hsiang Chung, Wen-Sheng 應用化學系 Department of Applied Chemistry |
關鍵字: | regioselectivity;fulvene;steric effect;inclusion complex;1,3-dipolar cycloaddition;chiral shift reagent;molecular reactor |
公開日期: | 31-七月-2006 |
摘要: | The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2 equiv of nitrile oxides 2a-d gave 1/1 cycloadducts, 3a-d and 4a-d, as the major products, and four other 1/2 minor cycloadducts 5-8a,b. The ratios of 1/1 cycloadducts 3a-d to 4a-d in THF solution were about 1/1 in the four different nitrile oxides 2a-d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in beta-cyclodextrin (beta-CD) aqueous solution compared to that of 40/60 in the absence of P-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with beta-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of beta-CD. The binding constant of 1 center dot beta-CD in acetone-d(6)/D2O (1/1) was determined to be 188 +/- 9 M-1 by H-1 NMR titration experiments. The binding mode of 1 center dot beta-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1 center dot beta-CD, 3a center dot beta-CD, 4a center dot beta-CD, 9a center dot beta-CD, and 9b center dot beta-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, beta-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in H-1 NMR. (c) 2006 Elsevier Ltd. All rights reserved. |
URI: | http://dx.doi.org/10.1016/j.tet.2006.05.021 http://hdl.handle.net/11536/12003 |
ISSN: | 0040-4020 |
DOI: | 10.1016/j.tet.2006.05.021 |
期刊: | TETRAHEDRON |
Volume: | 62 |
Issue: | 31 |
起始頁: | 7380 |
結束頁: | 7389 |
顯示於類別: | 期刊論文 |