room temperature, with BF 3 O(Et) 2 as the catalyst. The macrocycles TPns and QPns
were prepared in relatively high yields of 41% and 35%, respectively. In addition,
the monomers are easily prepared using commercial reagents by highly efficient
Suzuki coupling reaction.
12.3 Functionalized Biphen[n]arenes
Functionalization of macrocyclic receptors is very important in molecular recognition and self-assembly because it can change the solubility and physical/chemical properties of the macrocycles. Especially, water-soluble macrocycles are
significantly important for biological, environmental, and analytical applications
[34–37]. Per-alkoxy and per-hydroxy substituted biphen[n]arenes are not water
soluble. Therefore, the host–guest recognition of biphen[n]arenes is almost
always studied in organic solvents. However, one of the important advantages
of biphen[n]arenes is their versatile functionality because they have reactive
hydroxyl groups on both cavity portals. In this section, the syntheses of watersoluble biphen[n]arenes containing anionic or cationic groups on both rims are
introduced.
12.3.1 Anionic Water-Soluble 44BPns
Biphen[n]arenes are essentially conveniently modified. The per-hydroxy
biphen-[n]arenes (44BPns-OH) could be quantitatively prepared by cleavage of
the ether groups through the reaction with excess BBr 3 . Due to their reactive
hydroxyl groups, functionalized biphenarene derivatives can be facilely prepared
through nucleophilic substitution reactions of 44BPns-OH and alkylating agents.
44BPns-OH have different molecular recognition properties in comparison with
alkoxy-substituted hosts; they are insoluble in low-polarity solvents such as CHCl 3 ,
CH 2 Cl 2 , and toluene, but they have good solubility in acetone, acetonitrile, DMF,
and DMSO [38].
Water-soluble 4,4
0 -biphen[3]arenes (44CBP3) containing six carboxylate anions
were synthesized by Huang and our group simultaneously [39, 40]. Subsequently,
our group reported another water-soluble 4,4
0 -biphen[4]arene (44CBP4) bearing
eight carboxylato moieties [41]. As shown in Scheme 7, ethoxycarbonylmethoxysubstituted biphen[3]arene (44BP3-COOEt) was synthesized by the nucleophilic
substitution reaction of 44BP3-OH and ethyl bromoacetate in the presence of
base. Subsequent hydrolysis of the ethoxy moieties under basic conditions and
then acidification with HCl afforded the carboxylic acid-substituted biphen[3]arene
(44BP3-COOH) in very high yield (89%). The water-soluble 44CBP3 was further
obtained by reacting 44BP3-COOH with aqueous ammonia solution. The presence
of six negative charges makes it possible for this biphen[3]arene to act as a cation
receptor in water. The host–guest recognition and self-assembly of 44CBP3 are
introduced in the section “Cationic Water-Soluble 44CBP3.”
12 Biphen[n]arenes: Synthesis and Host–Guest Properties
317
were prepared in relatively high yields of 41% and 35%, respectively. In addition,
the monomers are easily prepared using commercial reagents by highly efficient
Suzuki coupling reaction.
12.3 Functionalized Biphen[n]arenes
Functionalization of macrocyclic receptors is very important in molecular recognition and self-assembly because it can change the solubility and physical/chemical properties of the macrocycles. Especially, water-soluble macrocycles are
significantly important for biological, environmental, and analytical applications
[34–37]. Per-alkoxy and per-hydroxy substituted biphen[n]arenes are not water
soluble. Therefore, the host–guest recognition of biphen[n]arenes is almost
always studied in organic solvents. However, one of the important advantages
of biphen[n]arenes is their versatile functionality because they have reactive
hydroxyl groups on both cavity portals. In this section, the syntheses of watersoluble biphen[n]arenes containing anionic or cationic groups on both rims are
introduced.
12.3.1 Anionic Water-Soluble 44BPns
Biphen[n]arenes are essentially conveniently modified. The per-hydroxy
biphen-[n]arenes (44BPns-OH) could be quantitatively prepared by cleavage of
the ether groups through the reaction with excess BBr 3 . Due to their reactive
hydroxyl groups, functionalized biphenarene derivatives can be facilely prepared
through nucleophilic substitution reactions of 44BPns-OH and alkylating agents.
44BPns-OH have different molecular recognition properties in comparison with
alkoxy-substituted hosts; they are insoluble in low-polarity solvents such as CHCl 3 ,
CH 2 Cl 2 , and toluene, but they have good solubility in acetone, acetonitrile, DMF,
and DMSO [38].
Water-soluble 4,4
0 -biphen[3]arenes (44CBP3) containing six carboxylate anions
were synthesized by Huang and our group simultaneously [39, 40]. Subsequently,
our group reported another water-soluble 4,4
0 -biphen[4]arene (44CBP4) bearing
eight carboxylato moieties [41]. As shown in Scheme 7, ethoxycarbonylmethoxysubstituted biphen[3]arene (44BP3-COOEt) was synthesized by the nucleophilic
substitution reaction of 44BP3-OH and ethyl bromoacetate in the presence of
base. Subsequent hydrolysis of the ethoxy moieties under basic conditions and
then acidification with HCl afforded the carboxylic acid-substituted biphen[3]arene
(44BP3-COOH) in very high yield (89%). The water-soluble 44CBP3 was further
obtained by reacting 44BP3-COOH with aqueous ammonia solution. The presence
of six negative charges makes it possible for this biphen[3]arene to act as a cation
receptor in water. The host–guest recognition and self-assembly of 44CBP3 are
introduced in the section “Cationic Water-Soluble 44CBP3.”
12 Biphen[n]arenes: Synthesis and Host–Guest Properties
317