The Development of A New Intramolecular Cyclization with the Organic Iron Complex

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In the presence of tetrabutylammonium tricarbonylnitrosylferrate [n-Bu_4N] [Fe(CO)_3NO] (TBAFe), 1,2-dienes (Allenes) reacted with Alkyl halides to give the corresponding (η^3-2-acylallyl) dicarbonylnitorosyliron complexes accompanied with acylmetallation. In this research, we investigate the development of the intramolecular cyclization by the reaction of ω-iodoalkylallenes with TBAFe accompanied with intramolecular acylmetallation as an advancement of the above reaction. ω-Iodoalkylallenes and TBAFe stirred at room temperature under argon for 15 h in dichloromethane and then, the reaction mixtures are chromatographed with silica gel to give the corresponding cyclic (η^3-2-acylallyl)dicarbonylnitrosyliron complexes. The yield of 5 and 6 membered rings are high and that of the 7 membered ring is very low. That of 8 membered ring is lower than that of 5 and 6 membered rings and higher than that of 7 membered ring. Then, the result cyclic π-allyliron complexes react with carbon nucleophiles at room temperature under argon in THF for 15 h. The reaction mixtures are chromatographed with silica gel to give the corresponding 2-alkyl-2-cycloalkenones in good yields. In results, a new synthetic method of some membered ring α,β-unsaturated cyclic enones is developed.