Chemistry Reference
In-Depth Information
1.
PS-BEMP
(1.5 equiv)
THF, rt
O
Ar
ArNH
2
+ RCOCl
N
H
R
2. polymeric trisamine
(5 equiv), rt
(2 equiv)
Cl
O
O
N
N
H
N
N
H
S
Cl
98%
99%
OPh
H
N
EtOOC
N
N
H
O
S
N
99%
89%
Scheme 6.1
Acylation of less reactive heterocyclic amines
alkylguanidine attached to polystyrene was used in the transesterification of triglycerides
[18]. Thereafter, similar works have appeared in the literature [19-23], andTBDanchored on
the mesoporous molecular sieve, MCM-41, has also been developed for the transesterifica-
tion of
-ketoesters [24].
On the other hand, Kim and Le reported that the use of PS-BEMPwas very convenient for
the N-acylation of several weakly nucleophilic heterocyclic amines with acyl chloride
(Scheme 6.1) [25]. In this example, treatment with polymer-based trisamine after comple-
tion of the reactionwith PS-BEMPwas convenient for removing excess acyl chloride. Thus,
the correspondingN-acylated compounds could be obtained in good yields and high purities
by simple filtration. The utility of PS-BEMP as an acid scavenger has also been established
in other types of transformations to make free amines from their salts [26].
Similarly, Ilankumaran and Verkade reported that PS-NPAPTworked well as a catalyst
(10mol%) for the acetylation of a variety of primary alcohols using vinyl acetate as an
effective acetylating agent even in the presence of acid labile groups within the molecule
[27]. This catalyst could be used three times without a significant loss of reactivity, but after
that it tended to decompose to a fine powder. Interestingly, this chemistry was recently
extended to the green chemical production of biodiesel from soybean oil via transester-
ification inmethanol using PS-N3PAPTas a catalyst at room temperature [28]. It was shown
that the catalyst could be recycled 11 times, although its activity decreased gradually with
time. Despite the extensive efforts to find clean and selective methods for the synthesis of
carbamates and unsymmetrical alkyl carbonates from diethyl carbonate, there are few
reports on the use of the mesoporous silica-supported TBD as a basic catalyst [29].
b
