REACTION OF ETHYL 3,3-DIETHOXYACRYLATE WITH FISCHER ALKOXYALKYNYL TRANSITION-METAL CARBENE COMPLEXES

The title reaction afforded various amounts of differently substituted pentacarbonyl pyranylidene complexes, depending on factors such as th e metal, substitution at the alkynyl moiety and relative ratio of the reagents employed. The results obtained are explained by a cycloadditi on-ring-opening mechanism giving intermediates that can further cycliz e to pyranylidene derivatives. The importance of the dialkoxy and este r groups in promoting this cyclization was studied by replacing ethyl 3,3-diethoxyacrylate by model compounds, such as 4,4-dimethoxybut-3-en -2-one and 2-[(methoxycarbonyl)methylidene]-1,3-dioxolane.