Disrotatory ring opening of cyclobutene-iron carbonyl complexes

Demoniac Intervention in the Thermal Electrocyclic Ring Opening of Cyclobutenes: Fe(CO)3 Complexation of Pericyclic Transition Structures

“…Nonetheless, despite dogged attempts [8], the stereoselectivity of Fe(CO) 3 -promoted ring opening for geometrically unfettered cyclobutenes has not been determined. The ring-opening reactions of Fe(CO) 4 complexes of strained tricyclic cyclobutenes [9] [10], which presumably lose CO to produce coordinatively unsaturated Fe(CO) 3 -cyclobutene complexes [9] [11], have been studied experimentally (representative examples are shown in the Scheme), but only disrotatory ring opening towards the metal is likely in these systems due to the geometric constraints imposed by the additional fused rings. We have investigated the ring opening of the parent Fe(CO) 3 -cyclobutene model system 2 ) using hybrid HF-DFT calculations to determine whether disrotatory ring opening towards the metal is in fact the preferred mode of ring opening in the absence of geometric constraints.…”

Transition metal catalyzed rearrangements of small ring organic molecules

“…An examination of the chemistry of these metals shows that Ag(l) complexes strongly with benzene, while no nickel aromatic complexes are known.22 In contrast, Ni(ll) and Pd(ll) form strong metal-olefin bonds, while Ag(l) binds only weakly without the presence of electron-withdrawing substituents on the olefin. Recently, support for the intermediate complex was received, when Pettit, et al 23 showed the rearrangement of a number of iron-complexed cyclobutenes to butadienes. orbital symmetry.27•28 In the Woodward-Hoffmann27 formalism, disrotatory opening is symmetry forbidden, while in the bicyclic molecules conrotatory opening is inhibited since it leads to an even more highly strained product.…”

Total Syntheses of Guanacastepenes N and O

“…[15] Electrocyclic ring opening of cyclobutenes mediated by [Fe 2 (CO) 9 ] has been limited to simple hydrocarbons. [16] To the best of our knowledge, the conversion of 12 into 13 is the first application of this iron-mediated process in a complex setting. The implemented cyclohexyne insertion allowed access to the tricyclic core of the guanacastepenes in only nine steps from commerically available material.…”