Preparation, Characterization, and Reactivity of (3-Methylpentadienyl)iron(1+) Cations

The title cations (9 and 12) were prepared by dehydration of (3-methyl-2,4-pentadien-1-ol)Fe(CO)2L+
complexes. The structure of the (CO)2PPh3-ligated 12 was determined by single-crystal X-ray analysis.
Reaction of carbon and heteroatom nucleophiles to (3-methylpentadienyl)Fe(CO)3+ cations 9 and 12
proceeds either via attack at the dienyl terminus to give (3-methyl-1,3Z-diene)iron complexes or via
attack at the internal carbon, followed by carbon monoxide insertion and reductive elimination to afford
3-methyl-4-substituted cyclohexenones. Cyclohexenone formation was found to be prevalent for addition
of stabilized nucleophiles with strongly dissociated counterions to cation 9 (L = CO). Reaction of cation
9 with sodium bis[(−)-8-phenylmenthyl] malonate gave a single diastereomeric cyclohexenone.