Dynamic Diastereoselectivity during Iron Carbonyl Mediated Spirocyclization Reactions

Dynamic diastereoselectivity during Fe(CO)<sub>3</sub> promoted [6 + 2] ene spirocyclization of <b>35a</b> and <b>35b</b>, having a chiral center on the pendent side chain, was investigated and gave rise to products <b>28a</b> and <b>28b</b> instead of four possible isomers. From this reaction, two chiral centers are generated, with absolute stereochemistry determined by the double bond geometry and the chiral center already present. <b>28a</b>/<b>b</b> and the diene product from demetallation of <b>28a</b> are proposed as potential intermediates for total synthesis of 18-deoxycytochalasin H. Furthermore, a stepwise second cyclization and a tandem double cyclization mediated by the Fe(CO)<sub>3</sub> moiety was investigated.