Macrocyclic Ligands - Web del Profesor

Me
2.4.4 Calixarenes
O
Me
OMe
OMe MeO
O
(22)
Calixarenes (23) are the macrocyclic result of condensations
between phenols and formaldehyde 37 and have been
referred to as the most easily accessible molecular basket. 38
t-Bu
t-Bu
OH
OH HO
OH
t-Bu
(23)
H 2N
H2N
O
NH
H
N
HN
Me
t-Bu
NH 2
NH2
NH
NH
NH
NH
3 SYNTHESIS
3.1 Polyaza Macrocycles
MACROCYCLIC LIGANDS 5
3.1.1 Conventional (Nontemplate) Syntheses
Reviews of synthetic procedures can be found for tridentate
and pentadentate macrocyclic ligands with nitrogen donors,
mixed nitrogen donors, and sulfur donor macrocycles, 39 the
techniques of which can be expanded to other ring sizes. The
general procedures will be summarized below.
Cyclic secondary amines, [n]aneNm, are generally prepared
by macrocyclization reactions known as the Richman–Atkins
procedure. 40 These reactions involve ring closure by
condensation of two precursor fragments of the cyclic
molecule. In general, one fragment consists of a salt
of a sulfonamide, while the other contains two terminal
leaving groups, which can vary in identity and include
chloride, bromide, hydroxide, or, more often, a sulfonate ester
(Scheme 1). The reaction is performed in polar aprotic solvents
and may involve high dilution techniques. Simplified routes
to tri-, tetra-, and pentaaza systems have been described. 41 A
handy synthetic technique for the smaller triaza ring has been
described by Alder, where the macrocycle is built by using
a single carbon as template. 42 Treatises on the synthesis of
pyridine-containing macrocycles 43 and imidazole-containing
macrocycles 44 have also been reported.
Functionalized macrocycles (5) with additional ligating
components attached as pendant arms have been an area
of focus in efforts to expand the chemistry of macrocyclic
receptors by incorporating additional recognition sites.
Synthetic techniques for N-functionalized, C-functionalized,
NTs
TsN −
Scheme 1
Ts
N
TsN
OMs MsO
HN
NTs TsN
HN
HN
− NTs