[3 + 2] cyclopentane annulation reactions using organoiron reagents

Article abstract of DOI:10.1021/om00072a025

The allyl ligand in the organoiron complex 1, (η¹-allyl)Fp [Fp = (η⁵-C₅H₅)Fe(CO)₂], serves as a C₃ dipolar synthon in aluminum bromide catalyzed reactions with cyclohexenone and by itself with 2-carbethoxy-cycloalkenones, affording cyclopentane annulation products. The structural limitations of these reactions with respect to substitution of the enone and the organometallic reagent have been examined. The acetylenic ligand in (η¹-2-butynyl)Fp similarly underdoes aluminum bromide catalyzed [3 + 2] cycloaddition reaction with cyclohexenone, but (η¹-1-propynyl)Fp yields instead the product of [2 + 2] cycloaddition.