ACID-CATALYZED AND BASE-CATALYZED ANTI TO SYN ISOMERIZATION OF (DIENONE)TRICARBONYLIRON COMPOUNDS

(Dienone)tricarbonyliron compounds which have anti acyl groups rearrange quantitatively to their syn isomers in the presence of strong acids or bases. In methanol the reactions are first order in methoxide or methyloxonium ion. Introduction of substituents on diene carbons causes only small rate changes, but substitution of triphenylphosphine for CO slows isomerization drastically. Isomerization in methanol-O-d proceeds with ca. 40% deuterium incorporation α to the carbonyl group. These observations lead to the conclusion that rate-determining nucleophilic attack of methoxide (or methanol) at iron produces an intermediate which is capable of rapid isomerization and deuterium incorporation. Dienonitrile complexes undergo H-D exchange at Cα with retention of configuration by a different mechanism. © 1979, American Chemical Society. All rights reserved.