Catalyst‐Free Electrophilic Ring Expansion of N‐Unprotected Aziridines with α‐Oxoketenes to Efficient Access 2‐Alkylidene‐1,3‐Oxazolidines.

2‐(2‐Oxoalkylidene)‐1,3‐oxazolidine derivatives were synthesized in good to excellent yields regiospecifically through the catalyst‐free electrophilic ring expansion of N‐unprotected aziridines and the ketene C=O double bond of α‐oxoketenes, in situ generated from the microwave‐assisted Wolff rearrangement of 2‐diazo‐1,3‐diketones. The ring expansion predominantly underwent an SN1 process and the hydrogen bond decides the (E)‐configuration of products. [ABSTRACT FROM AUTHOR]