Department of Chemistry
Todd Wehr Chemistry, 101
1414 W Clybourn St.
Milwaukee, WI 53233
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Ph.D., Dartmouth College
B.A., Wesleyan University
The reaction of acyclic pentadienyl iron cations (1) with nucleophiles may proceed either at the terminal carbon atoms (path a) and/or at internal positions (path b). The regioselectivity of these reactions depend on the substitutents present on the pentadienyl ligand, the "spectator" ligands attached to iron, and the nature of the nucleophile (ie. heteroatom nucleophiles, or organolithiums, or stabilized carbon nucleophiles), and in certain cases, the nucleophile counterion. (Diene)iron products (2) produced by “path a” are stable, isolable species in which the iron serves as a protecting group for the diene against oxidation, reduction and cycloaddition reactions; decomplexation under oxidative conditions generates the free ligand. (Pentenediyl)iron products produced by “path b”, which bear an electron withdrawing group at C1 (3a) are also stable, isolable species, however decomplexation of these (pentenediyl)iron complexes, via an oxidatively induced-reductive elimination, gives vinylcyclopropanecarboxylates. Additionally, if an alkenyl nucleophile is used, the resultant divinylcyclopropanes may undergo Cope rearrangement to give cycloheptadienes. In contrast, (pentenediyl)iron complexes without an electron withdrawing group at C1 (3b) are unstable and undergo carbon monoxide insertion and reductive elimination to generate cyclohexenones. Thus, the acyclic (pentadienyl)iron(1+) cations serve as a versatile precursor to conjugated dienes, cycloheptadienes, vinylcyclopropanes and cyclohexenones.
We have utilized this reactivity to prepare a variety of natural and non-natural product targets as indicated in Scheme 2.
The use of simple, relatively inexpensive hydrocarbons as starting materials for the synthesis of complex molecules relies on efficient methods for their oxidation, rearrangement and/or functionalization. We have utilized cyclohexadiene as a precursor for a stereochemically diverse spectrum of polyhydroxyaminocyclohexanes (aminocyclitols, Scheme 3). In addition, reaction of (cyclooctatetraene)iron (4) with a variety of electrophiles generates isolable (dienyl)iron cations (5a and b, Scheme 4).
Professor Donaldson received his B.A. in 1977 from Wesleyan University and his Ph.D. degree in organometallic chemistry from Dartmouth College in 1981. He was a Postdoctoral Research Associate at Brandeis University (1981-82) and a Visiting Assistant Professor at Wesleyan (1982-83) before joining the faculty at Marquette University in August 1983. Professor Donaldson was awarded the Edward D. Simmons Award for Junior Faculty Excellence (1988), the Rev. John R. Raynor Faculty Award for Teaching Excellence (1995), and a Alexander von Humboldt Research Fellow at Philipps- Universitaet Marburg, Germany (1990-91). He was a visiting Professor of the University of Strathclyde (Glasgow) for Jan-June 2015 and Feb-March 2019.