Reactions of Epoxides, Thiiranes, Aziridines and Azirines with Cyanoform

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.