Search

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]

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans -3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis -thiiranes through an intramolecular S N 2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis -3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis -oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively. [ABSTRACT FROM AUTHOR]

Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines has been achieved via reactions of thiiranes and α-diazo-β-1,3-dicarbonyl compounds under microwave and copper sulfate-assisted conditions. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-1,4-oxathiines from readily available thiiranes and trans -3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis -thiiranes. The reaction mechanism was also proposed. [ABSTRACT FROM AUTHOR]