TY - JOUR
T1 - Conformations and Structures of Tetra- O -alkyl-p-tert -butylcalix[4]arenes. How Is the Conformation of Calix[4]arenes Immobilized?
AU - Iwamoto, Koji
AU - Araki, Koji
AU - Shinkai, Seiji
PY - 1991/8/1
Y1 - 1991/8/1
N2 -
p-tert-Butylcalix[4]arene (1H
4
) was tetra-O-alkylated with alkyl halogens (RX: R = Me, Et, n-Pr, and n-Bu) in the presence of NaH as base, and the products (1R
4
) were analyzed by HPLC and
1
H NMR spectroscopy. It was found that (i) ring inversion is suppressed by R greater than Et, (ii) the final conformer distribution in 1Pr
4
and 1Bu
4
, is governed by the kinetic control, the main products being “cone” and “partial cone” (approximately in a 1:1 ratio), (iii) 1Me
4
mostly exists as a thermodynamically stable partial-cone conformer, and (iv) 1Et
4
shows an intermediary behavior between 1Me
4
and 1Pr
4
: it mostly exists as a partial-cone conformer but slowly isomerizes to a “1,2-alternate” conformer at high temperature. The X-ray crystallographic analysis of partial-cone-1Et
4
was investigated. To clarify where and how the conformation of 1R
4
is immobilized, we alkylated 1H
4
in a stepwise manner. It was shown that when NaH is used as base, the conformation of 1Et
4
is determined at the fourth ethylation step (1HEt
3
→ 1Et
4
), whereas the conformation of 1Pr
4
is determined at the third propylation step (1H
2
PR
2
→1HPr
3
). The conformer distribution was significantly affected by alkali and alkaline earth metal cations used as base; in particular, it is worthy of mentioning that (i) when Cs
2
CO
3
is used as base, 1,2-alternate- 1Pr
4
is formed in addition to partial-cone-1Pr
4
and (ii) when Ba(OH)
2
is used as base, cone-1Pr
4
is yielded in 100% selectivity. On the basis of these studies, we discuss how the conformation of calix[4]arenes is immobilized.
AB -
p-tert-Butylcalix[4]arene (1H
4
) was tetra-O-alkylated with alkyl halogens (RX: R = Me, Et, n-Pr, and n-Bu) in the presence of NaH as base, and the products (1R
4
) were analyzed by HPLC and
1
H NMR spectroscopy. It was found that (i) ring inversion is suppressed by R greater than Et, (ii) the final conformer distribution in 1Pr
4
and 1Bu
4
, is governed by the kinetic control, the main products being “cone” and “partial cone” (approximately in a 1:1 ratio), (iii) 1Me
4
mostly exists as a thermodynamically stable partial-cone conformer, and (iv) 1Et
4
shows an intermediary behavior between 1Me
4
and 1Pr
4
: it mostly exists as a partial-cone conformer but slowly isomerizes to a “1,2-alternate” conformer at high temperature. The X-ray crystallographic analysis of partial-cone-1Et
4
was investigated. To clarify where and how the conformation of 1R
4
is immobilized, we alkylated 1H
4
in a stepwise manner. It was shown that when NaH is used as base, the conformation of 1Et
4
is determined at the fourth ethylation step (1HEt
3
→ 1Et
4
), whereas the conformation of 1Pr
4
is determined at the third propylation step (1H
2
PR
2
→1HPr
3
). The conformer distribution was significantly affected by alkali and alkaline earth metal cations used as base; in particular, it is worthy of mentioning that (i) when Cs
2
CO
3
is used as base, 1,2-alternate- 1Pr
4
is formed in addition to partial-cone-1Pr
4
and (ii) when Ba(OH)
2
is used as base, cone-1Pr
4
is yielded in 100% selectivity. On the basis of these studies, we discuss how the conformation of calix[4]arenes is immobilized.
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U2 - 10.1021/jo00016a027
DO - 10.1021/jo00016a027
M3 - Article
AN - SCOPUS:21244492862
VL - 56
SP - 4955
EP - 4962
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 16
ER -