Dynamic diastereoselectivity during iron carbonyl mediated spirocyclization reactions

Dynamic diastereoselectivity during Fe(CO)3 promoted 6+2] ene spirocyclization of 35a and 35b, having a chiral center on the pendent side chain, was investigated and gave rise to products 28a and 28b 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. 28a/b and the diene product from demetallation of 28a 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)3 moiety was investigated.