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N
NC
p
-TsOH
CN
NC
H
NC
NH
2
539a
N
OMe
R
N
NC
p
-TsOH
538a;
R = H
538d;
R = OMe
NC
H
539d
SCHEME 10.91.
remarkable aziridination method, this reagent can be more conveniently accessed
through the oxidation of commercially available diaminomaleonitrile with DDQ.
Another potential drawback to the wider use of diiminosuccinonitrile (
527
) is its
pronounced toxicity towards mammals (ALD
¼
90mg/kg in rats).
10.9 INTRAMOLECULAR ALKENE ADDITION OF STABILIZED
NITRENIUM IONS
Notwithstanding some elegant solutions to this longstanding problem,
207
the inher-
ent charge density associated with the oxygen atom of amide groups presents a major
obstacle to the preparation of lactams
via the electrophile-promoted cyclo-
functionalization of alkenes, since iminolactones
554
are the kinetically favored
products. In this context, the intramolecular reaction of acyl nitrenium ions
553
with
alkenes offers a unique, if underappreciated, strategy for the preparation of func-
tionalized lactams, which overcomes many of the shortcomings inherent to halo-
lactamization (Scheme 10.92). Since, during intramolecular nitrenium-alkene
additions reactions, ring formation is reliant upon a process that generates two
C
555
, the question
“lactone or lactam?” can be replaced by ones regarding the formation and subsequent
ring opening of a bicyclic aziridinium ion intermediate
N bonds, rather than on the cyclization of a halonium ion
552
556
.
ınguez and coworkers have carried out extensive studies of the intramolecular
reaction of aryl nitrenium ions and have reported that upon treatment with PIFA,
N
-
p-
methoxyphenyl (PMP)-substituted pent-4-enamides
Dom
559
undergo diastereoselective
5-
exo-trig
cyclization to yield pyrrolidinones
, the products of alkene trifluor-
oacetoxyamidation.
208
In light of their instability, these compounds were hydrolyzed
and the resulting alcohols immediately reduced with borane to the corresponding
derivative pyrrolidine derivatives
562
564
, which were isolated in good yield, albeit with
