catalysts often suffer from low efficiency because of reduced
homogeneity during the reaction. Consequently, various
methods using soluble supports have been developed: hy-
perbranched polymers,6 dendrimers,7 and hybrid materials,8
or tagging of the catalyst to the solid or soluble supports.9
We have developed a new solvent system consisting of 4,4′-
bipyridyl and phenol, for recycling catalysts of chelation-
assisted hydroacylation of olefins with primary alcohols.10
Although this solvent system exhibited a good reactivity and
an easy separation of the rhodium catalyst and 2-amino-4-
picoline from the product ketone for the recycling catalysis,
this catalytic system has the limitation of partial leaching of
the organic catalyst, 2-amino-4-picoline. Recently, we de-
veloped a recyclable supported catalyst system for recycling
a rhodium complex for orthoalkylation using a hydrogen-
bonding self-assembly motif consisting of a barbiturate
bearing a phosphine ligand and 5-hexyl-2,4,6-triaminopyri-
midine.11 Here, we wish to report a new recyclable self-
assembly catalyst system for chelation-assisted hydroacyla-
tion of olefin with primary alcohol.
Scheme 1. Barbiturate-Substituted 2-Aminopyridine (1a),
Triphenylphosphine (1b), and Its Interaction with
5-Hexyl-2,4,6-triaminopyrimidine (2a)
The barbiturate is known to form a supramolecular
assembly with 2,4,6-triaminopyrimidine through six hydro-
gen bondings per molecule.12 Therefore, we expected that
the barbiturate 1a bearing a 2-aminopyridin-4-yl group as a
chelation auxiliary would lead to the formation of a
hydrogen-bonding self-assembly with 5-hexyl-2,4,6-triami-
nopyrimidine (2a), which can serve as a support for recycling
the organic catalyst (Scheme 1).
The barbiturate 1a was prepared in several steps (Scheme
2). First, compound 3 bearing a propargyl group was
prepared from diethyl ethylmalonate and propargyl chloride.
This was followed by a barbiturate formation with urea.
2-Aminopyridine derivative 4, having an azido group, was
also prepared by functionalization of amine-protected 2-amino-
4-picoline. Copper(I)-catalyzed [2 + 3] dipolar cycloaddition
of 3 and 4 was achieved in the presence of CuSO4‚5H2O
and Na-ascorbate to afford 1a via “click chemistry”.13 The
barbiturate 1b was also prepared by the literature method11
with slight modification: a nucleophilic addition of diethyl
ethylmalonate on the 4-benzyl bromide group of triphen-
Scheme 2. Synthesis of 1a and 1b
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