RING-FUSED AND SPIRO CYCLOPENTENONES BY NI(CO)4-PROMOTED INTERMOLECULAR CARBONYLATIVE CYCLOADDITION OF ACETYLENES WITH 3-HALOCYCLOALKENES AND 1-(HALOMETHYL)CYCLOALKENES

The title carbonylative cycloaddition of five- to eight-member ring 3-halo- and 1-(halomethyl)cycloalkenes with different acetylenes was studied. From moderate to good yields of ring-fused and spiro cyclopentenone derivatives were obtained, especially in the reaction with acetylenes bearing electron-withdrawing substituents by proper selection of the reaction conditions to avoid the acetylene polyinsertion and/or other side reactions from the organonickel intermediates. In this context, the beneficial role of acetate ion on the outcome of the reaction is rationalized. This process leading to the formation of bicycloadducts with the concomitant formation of up to six C-C bonds, with high regio- and stereoselectivity, can be useful in the synthesis of natural products as exemplified by the easy preparation of [5-5-5] tricyclic compound 14 from a 1:1 cis and trans isomeric mixture of 6-acetoxy-3-bromocyclooctene (11). A plausible general reaction mechanism is proposed that is consistent with all the products obtained.