Sequenced reactions with samarium(II) iodide. Sequential intermolecular carbonyl addition intramolecular nucleophilic acyl substitution for the preparation of seven-, eight-, and nine-membered carbocycles

Samarium(II) iodide has been employed to promote a tandem intermolecular carbonyl addition/intramolecular nucleophilic acyl substitution sequence, generating seven- through nine-membered monocyclic, bicyclic, and tricyclic ring systems with good yields and high diastereoselectivities. This tandem reaction consists of an intermolecular reaction followed by an intramolecular ring expansion that results in a formal [m + n] cycloaddition, starting from extremely simple, readily available substrates. The regioselectivity and stereoselectivity of the process arise from a tuning of the reducing power of samarium(II) iodide with nickel(II) iodide in the first step and irradiation with visible light in the second. By using this method, a variety of structural motifs have been assembled rapidly in good yields.