Banert K.
*
Korb M,
Chityala M.
Technische Universität Chemnitz, Germany
Ring Enlargement of Three-Membered Heterocycles by Treatment with In Situ Formed Tricyanomethane.
Chem. Eur. J. 2020;
26: 6158-6164
Key words
tricyanomethane - thermolysis - ring enlargement - epoxides - aziridines - push–pull
alkenes
Significance
Vinyl azide 1 can be prepared on a gram scale, is safe to handle at room temperature, and can be
stored in the solid state at –25 °C. Oxazolidines, thiazolidines, and imidazolidines
are useful pharmacophores (S. Sasho et al. Chem. Pharm. Bull. 2009, 57, 288; M. Takagi T. Nishibe, K. Ishimitsu WO 2003000668, 2003) and have been prepared by other methods (L. G. Chanu, O. M. Singh, S. H. Jang, S.
G. Lee Bull. Korean Chem. Soc. 2010, 31, 859; A. Samzadeh-Kermani Monatsh. Chem. 2016, 147, 761). However, previous preparations are limited by lack of commercial availability
of reagents. The present method increases the scope of accessible derivatives of these
heterocycles; electrophiles can be prepared using well-known procedures such as epoxidation
or aziridination.
Comment
The regio- and stereochemical outcome of the reaction is consistent with the conventional
acid-catalyzed epoxide ring-opening process. Under similar conditions, the reaction
of cyanoform (2) or tricyanomethanide salts with other electrophiles (alkyl halides, ketones, Michael
acceptors) results in C-alkylation (K. Rakus, S. P. Verevkin, H.-D. Beckhaus, C. Rüchardt
Chem. Ber. 1994, 127, 2225; K. Banert et. al. Angew. Chem. Int. Ed. 2017, 56, 9582). The observed N-alkylation reported here suggests a ketenimine intermediate
in this transformation. The proposed mechanism is supported by 15N-labelling of the electrophile (azirine) or nucleophile (1) to confirm the regiochemistry of the nucleophile addition as shown.
