Iron‐Catalyzed Coupling of Tricyclo[4.1.0.0 2,7 ]hept‐1‐ylmagnesium Bromide and Related Grignard Reagents with Propargylic and Allylic Halides

Several uncatalyzed and transition metal‐catalyzed cross coupling reactions of the Grignard compounds 1c or 2c with propargylic or allylic halides were investigated. Fe(acac) 3 was the most effective catalyst for the preparation of allyl‐and propargylbicyclo[1.1.0]butanes 7 and 5 . In the latter case, the formation of the isomeric allenylbicyclo[1.1.0]butanes 6 was also observed. Stereoelectronic factors of substituents like a trimethylsilyl group as a directing group could be utilized for the formation of either 5 or 6 . A number of bicyclo[1.0.0]butanes 15–21 with two substituents in the bridgehead positions were accessible by that route as well. In the case of the bis‐allenyl compound 24c , an ene‐type reaction leading to the first known derivative of a [4.1.1]propella‐2,4‐diene 25 was observed. Base‐catalyzed isomerizations of the propargylbicyclo[1.1.0]butanes 5 opened a new route to alkynylbicyclo[1.1.0]butanes 30–32 .