Reaction of ethyl 3,3-diethoxyacrylate with Fischer alkoxyalkynyl transition metal carbene complexes

Article abstract of DOI:10.1016/0022-328X(94)05369-M

The title reaction afforded various amounts of differently substituted pentacarbonyl pyranylidene complexes, depending on factors such as the metal, substitution at the alkynyl moiety and relative ratio of the reagents employed.The results obtained are explained by a cycloaddition-ring-opening mechanism giving intermediates that can further cyclize to pyranylidene derivatives.The importance of the dialkoxy and ester 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.Keywords: Carbene complexes; Pyranylidene complexes; Chromium; Synthesis; X-ray structures