TETRAHEDRON
LETTERS
Tetrahedron Letters 41 (2000) 9939–9942 Pergamon
Addition of silylated carbon nucleophiles to iminium and
cyclic N -acyliminium ions promoted by InCl
3
Dennis Russowsky,
a,
* Roge ´rio Zen Petersen,
a
Marla Narciso Godoi
a
and
Ronaldo Aloise Pilli
b
a
Instituto de Quı ´mica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501 -970, Brazil
b
Instituto de Quı ´mica, Universidade Estadual de Campinas, Campinas, SP 13083 -970, Brazil
Received 29 September 2000; revised 16 October 2000; accepted 19 October 2000
Abstract
InCl
3
was used as Lewis acid in the addition of silyl enolates and allyltrimethylsilane to aromatic
aldimines and cyclic N -acyliminium ions derived from 5-acetoxylactams affording -aminocarbonyl
systems and allyl adducts, respectively, in reasonable to good yields. The diastereofacial selectivity of
cyclic N -acyliminium ions was investigated. © 2000 Elsevier Science Ltd. All rights reserved.
The Mannich reaction is a powerful tool in the construction of -aminocarbonyl systems.
1–4
In the bimolecular version
1
of the classical Mannich reaction, the use of preformed or in situ
generated iminium
5
or N -acyliminium ions
6,7
and carbon nucleophiles has greatly expanded the
versatility of this methodology allowing the use of milder reaction conditions and the introduc-
tion of elements of regio- and stereoselective control.
The intensive research on new types of Lewis acids as activating agents, e.g. zirconium
8
and
palladium
9
complexes and rare earth triflates,
10
in aldol-type Mannich reaction has enlarged the
field of its applications.
Recently, the use of InCl
3
as a Lewis acid in a multicomponent aldol-type Mannich reaction
in aqueous media
11,12
was reported. However, the aqueous media protocol lacks generality due
to the lower solubility and/or stability of the reactants and products.
Despite the use of InCl
3
in a three-component Mannich reaction, to the best of our knowledge
there has been no report on the employment of InCl
3
to promote the generation of iminium ions
from aldimines and/or cyclic N -acyliminium ions to carry out the bimolecular aldol-type
Mannich reaction.
This prompted us to disclose our preliminary results using InCl
3
as an activating agent of
aromatic aldimines as well as to promote the generation of cyclic N -acyliminium ions and their
reactions with silylated carbon nucleophiles in organic media.
* Corresponding author. E-mail: dennis@iq.ufrgs.br
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII:S0040-4039(00)01828-1