Chiral ionic liquids are quite attractive for their potential application to chiral discrimination (b) low melting points(c) good chemical stability towards water and commonorganic substrates and(d) relatively low viscosity and good thermal stability

Chiral ionic liquids are quite attractive for their potential application to chiral discrimination (b) low melting points(c) good chemical stability towards water and commonorganic substrates and(d) relatively low viscosity and good thermal stability
Chiral ionic liquids are quite attractive for their potential application to chiral discrimination
(b) low melting points
(c) good chemical stability towards water and common
organic substrates and
(d) relatively low viscosity and good thermal stability.
Howarth and co-workers have described the use of chiral
imidazolium cations in Diels–Alder reactions.55 The
synthesis of these systems,however,required an expensive
chiral alkylating agent.The use of ionic liquids with chiral
anions is somehow more obvious,since some of these are
readily available as sodium salts.56 Ionic liquids (12a,b) of
the type 1 (Fig.6) were prepared by alkylation of the
corresponding oxazoline with an alkyl bromide followed by
anion exchange.Although ionic liquids of the type 1 can be
prepared on a multigram scale,the relatively low overall
yield of the four-step synthesis is a concern for the practical
use of type 1 ionic liquids.Moreover,the oxazolinium
cation has a low stability under acidic conditions and ring
opening occurs to a large extent.These considerations led to
the development of a room temperature ionic liquid of the
type 2 (Fig.7),which is more readily obtained from the
alkaloid ephedrine in a three-step synthesis.A Leuckart–
Wallach reaction,followed by alkylation with Me2SO4 and
ion exchange in aqueous solution,gave the ionic liquid of
type 2 in 80% yield with a melting point of 54 8C.
A further quest for room temperature ionic liquids with
chiral cations resulted in the synthesis of an ionic liquid of
the type 3 (Fig.7) in a very similar manner to type 2 in an
overall yield of 75%.The enantiopurity of 12a was
confirmed by 19F NMR spectroscopy after basic hydrolysis
of 12a and reaction with (S)-Mosher’s acid chloride.The
enantiopurity of type 2 and type 3 was confirmed by 19F
NMR spectroscopy after esterification of type 2 and type 3
with (S)-Mosher’s acid chloride.
Imidazolium salts with a cyclophane-type planar chirality
13–15 form a novel class of chiral ionic liquids,which
Figure 7.

Chiral ionic liquids are quite attractive for their potential application to chiral discrimination (b) low melting points(c) good chemical stability towards water and commonorganic substrates and(d) relatively low viscosity and good thermal stability
(b)低的熔点
(三)具有良好的化学稳定性对水和常见的
有机载体和
(d)相对低粘度和热稳定性.
Howarth和同事已经描述了使用手性
在Diels-Alder reactions.55 imidazolium阳离子
这些系统的合成,然而,需要一种昂贵
手性烷基化剂.离子液体的使用和手性
不知何故阴离子更明显,因为其中的一些
现成的如钠salts.56离子液体(12a,b)
1型的(图6)制备烷基化
相应的恶唑啉与紧随其后的烷基溴化
阴离子交换.虽然离子液体的1型糖尿病可以
口径multigram规模、相对较低的整体
四步合成产量关心的实用
使用1型离子液体.此外,oxazolinium
阳离子较低的下的稳定性和酸性环境下戒指
打开发生在很大程度上.这些因素导致
开发的一种室温离子液体
2型(图7),这是更容易得到
生物碱麻黄素在三个合成.一个Leuckart -
Wallach,其次是烷基化反应与Me2SO4
离子交换水溶液中,给了离子液体的
2型80%的熔点收率随54暖.
进一步探索室温离子液体
手性阳离子合成了离子液体的
3型(图7)在一个非常相似的方式二型的
总收率为75%.enantiopurity 12a的的
核磁共振光谱学确认后19F基本纤维素
12a的反应和(S),-Mosher酸的效果.这
enantiopurity 2型和类型19F已经确认了3
核磁共振光谱学酯化反应的后2类及式3
-Mosher(S)酸的效果.
Imidazolium盐与cyclophane-type平面手性
13 - 15形成一个小说类,手性离子液体
图7.