Beilstein J. Org. Chem. 2020, 16, 607–610.
tions with alcohols and thiols (which earlier gave a remarkable reactions are rapid, albeit moderately yielding. Despite the latter
improvement of the product yields of NH-insertion reactions drawback, the range of 1,3-disubstituted 2-pyrrolidones attain-
[2]) resulted in no notable improvement in this case.
able via the intermediate formation of α-diazo-γ-butyrolactams
was substantially expanded, thereby making this approach more
The only attempt to employ an aliphatic amine, cyclopropyl- useful for potential medicinal chemistry exploration of these
amine (which would presumably be less reactive in the RhII- disubstituted γ-lactams.
catalyzed insertion reaction [2]) resulted in the formation of a
sole identifiable product – enamine 8a, isolated chromatograph-
ically from a complex mixture of unidentified byproducts. The
Supporting Information
formation of 8a (that was also observed previously, along with
Supporting Information File 1
the expected, saturated coupling product of the RhII-catalyzed
reaction of cyclopropylamine with N-phenyl-α-diazo-2-pyrroli-
done [2]) can be rationalized, as proposed previously [2], either
by the oxidation of diazolactam 6c to a respective ketone (a
process described in the literature for other α-diazocarbonyl
compounds [6]), followed by a nucleophilic attack of cyclo-
propylamine. Alternatively, the formation of the enamine prod-
uct could be envisaged via the reaction of the amine with bis-
hydrazone 5, which would have formed, if the N–H insertion
pathway was not sufficiently rapid. Both assumptions are in line
with the formation of the similar enamine coupling product 8b,
that we observed with 2,6-dimethylaniline. With this unreac-
tive, sterically hindered aromatic amine, 6c is likely to undergo
General experimental information, synthetic procedures,
analytical data and NMR spectra for the reported
compounds.
Acknowledgements
We are grateful to the Research Centre for Magnetic Reso-
nance and the Centre for Chemical Analysis and Materials
Research of Saint Petersburg State University Research Park for
the analytical data.
either the unwanted N2→O oxidation or dimerize to bis- Funding
hydrazone 5, whereupon the resulting intermediate would be This research was supported by the Russian Science Founda-
eventually trapped by the aniline to give 8b (Scheme 2). The tion (project grant 19-33-90016).
viability of either (or both) of these possibilities is currently in-
ORCID® iDs
vestigated. It should be noted that a similar Rh2(esp)2-cata-
lyzed reaction of one of the N-aryl-α-diazo-γ-butyrolactams 1
with 2,6-dimethylaniline previously gave an excellent yield of
the N–H insertion product [2].
Preprint
A non-peer-reviewed version of this article has been previously published
Conclusion
We demonstrated that the scope of α-diazo-γ-butyrolactams
being capable to undergo RhII-catalyzed X–H insertion reac-
References
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tive dimerization was previously observed. This was achieved
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1. Zhukovsky, D.; Dar'in, D.; Kantin, G.; Krasavin, M. Eur. J. Org. Chem.
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Scheme 2: Formation of the enamine coupling products 8a and b.
609