APPROACHES TO SELECTIVE ISOPRENOLOGATION VIA REACTIONS OF (ETA-3-ALLYL)FE(CO)4(+) WITH ALLYL NUCLEOPHILES

The reactions of substituted (eta-3-allyl)Fe(CO)4BF4 complexes 1 with various allyl-metals [M = SiMe3 (2), -SnBu3 (3) and -FeCp(CO)2 (4)] and dienolate derivatives [CH2 = C(CH3)CH = COM(OR) (M = Li, SiMe3)] have been investigated in search of a method for regio- and stereocontrolled allyl-allyl coupling. All three classes of allyl derivatives react with 1 in moderate to good yield with variable regioselectivity; the silyl derivatives 2 generally provide good regioselectivity for attack at the less substituted terminus of unsymmetrical derivatives of 1 but deprotonation of the 1,1-dimethylallyl complex 1e prevents efficient isoprenylation. Although deprotonation of 1e also dominates with the siloxydienes, the lithium dienolates couple efficiently with 1; however, reaction at the alpha position of the dienolate dominates.