Regiodirecting effects in difunctionalised tricarbonyl[(1,2,3,4,5-η)-cyclohexadienyl]iron(1+) salts: building blocks for alkaloids

Electrophilic tricarbonyl[(1,2,3,4,5-eta)-cyclohexadienyl]iron(1+) salts that incorporate methoxy and 2-ethanoyl ester substituents have been prepared, and the regiochemistry of their reactions with nucleophiles in arylation reactions has been examined using the model nucleophile diphenylzinc. The 1-carbomethoxymethyl-2-methoxy salt 1 reacts selectively by the omega addition pathway, but the 2-carbomethoxymethyl-3-methoxy salt 9 gave a 6:1 mixture of omega and alpha addition products. The 1-carbomethoxymethyl-2-methoxy regioisomer 1 was prepared in >95% purity without recourse to chromatography and shows the correct regiocontrol for use as a starting material in organoiron-mediated routes to alkaloids such as lycorine and parkacine. (C) 2012 Elsevier Ltd. All rights reserved.