2+4 Cycloaddition reactions of neat dipivaloylketene

摘要

Various 2+4 hetero-Diels-Alder cycloddition reactions of dipivaloylketene (2) with polarized multiple bond systems are described. Aldehydes and ketones react with2to furnish 1,3-dioxin-4-ones7, imines and heterocumulenes (X=C=N) form 1,3-oxazin-4-ones9and11, respectively. Analogous reactions of2with ethyl vinyl ether, ethoxyacetylene, diethylcyanamide, and adamantanethione leading to 2 + 4 adducts12, 14, 15and16are also reported. All these cycloadditions proceed in high yield at very mild reaction conditions.