A different behaviour of the phthalimide ion in Srn1 reactions

Article abstract of DOI:10.3390/50300457

The phthalimide anion reacts by the S_RN1 mechanism under photostimulation)with different substrates. Whilst with 1-iodonaphthalene only reduction of the naphthyl radical is observed, with 1-iodoadamantane coupling at the carbon instead of at the nitrogen takes place.

Full text of DOI:10.3390/50300457

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Molecules 2000, 5
A Different Behaviour of the Phthalimide Ion in S 1 Reactions
rn
Manuel Bajo Maquieira, Alicia B. Peñéñory and Roberto A. Rossi
Departamento de Química. Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Cór-
doba. Ciudad Universitaria. (5000) Córdoba, Argentina
E-mail: manuelbm@dqo.fcq.unc.edu.ar; penenory@dqo.fcq.unc.edu.ar
Abstract: The phthalimide anion reacts by the S 1 mechanism under photostimulation
RN
with different substrates. Whilst with 1-iodonaphthalene only reduction of the naphthyl
radical is observed, with 1-iodoadamantane coupling at the carbon instead of at the nitrogen
takes place.
Introduction
The mechanism of Radical Nucleophilic Substitution (S 1) is a chain process with radicals and
RN
radical anions as intermediates [1]. Different substrates and nucleophiles participate in these reactions.
It is known that within the nitrogen-centered nucleophiles, aromatic amines react with aryl halides to
yield the substitution product on the carbon atom and none on the nitrogen atom. For example, the
photoinduced reaction of 2-naphthylamine with aryl halides renders mainly 1-aryl-2-naphthylamines
[
(
2]. However, the phthalimide ion (1) reacts with ter-butyl radicals yielding N-ter-butylphthalimide (2)
eq.1) [3].
Taking into account these results we began to study the photoinduced reactions of phthalimide ion
with different substrates.
O
O
SRN
1
N- + t-BuHgCl
N-Bu-t
(
72%) (1)
hν, DMSO
O
O
1
2
Results and Discussion
The photoinduced reaction of anion 1 with 1-iodonaphthalene (3) in dimethylsulfoxide (DMSO)
and in the presence of 18-crown-ether renders 72% of iodide ions after three hours and naphthalene is
the only product observed. This reaction does not occur in the dark.
The reaction of anion 1 with 1-iodoadamantane (4) under the same conditions, yields a 78% of io-

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Molecules 2000, 5
dide ions, adamantane (5) and the substitution products 6 and 7 which arise from the coupling reaction
of the adamantyl radical at the carbon 4 and 5 of anion 1 respectively. When this reaction was per-
formed in the presence of a radical trap as di-ter-butylnitroxide (di-t-BuNO) or a better electron ac-
ceptor than 4 as p-dinitrobenzene (p-DNB), results in strong inhibition. (eq.2). In the dark, no reaction
was observed between 1 and 4.
O
NH
I
O
DMSO
1
+
+
+
(2)
NH
O
O
4
5
6
7
hν
21%
12%
2.5%
<1%
-
45% (isolated)
2
0% di-t-BuNO 7%
18%
20%
-
2
0% p-DNB
3%
dark
-
These results showed that a photoinduced electron transfer from anion 1 to substrates 3 and 4 ren-
ders the naphthyl or the adamantyl radical intermediates respectively. While only hydrogen abstraction
is observed for the naphthyl radical yielding naphthalene as reduction product, the adamantyl radical
adds surprisingly to the carbon atoms instead of the nitrogen atom giving distonic radical anions. This
behavior is different from the previously described reaction of this anion with ter-butyl radicals [3]. In
the present communication we will discuss the reactivity of this anion with different substrates.
References and Notes
1.
Rossi, R. A.; Pierini, A. B.; Peñéñory, A. B. Recent Advances in the S 1 Reaction of Organic
RN
Halides. In The Chemistry of Functional Groups; Patai, S; Rappoport, Z., Eds.; John Wiley &
Sons: 1995; Chapter 24, p. 1395-1485.
2
.
.
Pierini, A. B.; Baumgartner, M.T.; Rossi, R. A. Tetrahedron Lett. 1987, 28, 4653.
Russell, G. A.; Khana, R. K. J. Am. Chem. Soc. 1985, 107, 1450.
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