title: Dehydropericyclic Reactions: Symmetry-Controlled Routes to Strained Reactive Intermediates.
abstract: The conceptual dehydrogenation of pericyclic reactions yields dehydropericyclic processes, which usually lead to strained or reactive intermediates. This is a simple scheme for inventing new chemical reactions. Computational results on two novel dehydropericyclic reactions are presented here. Conjugated enynes undergo a singlet-state photoisomerization that transposes the methylene carbon. We previously suggested excited-state closure to 1,2-cyclobutadiene followed by thermal ring opening. CCSD(T)//DFT computations show two minima of similar energy corresponding to 1,2-cyclobutadiene, one chiral and closed shell and the second a planar diradical. The chiral structure has a low barrier to ring opening and may best explain results on enyne photoisomerization. The first examples of 1,3-diyne + yne cycloadditions to give o-benzynes were reported in 1997. Computations on intramolecular versions of this tridehydro (-3H2) Diels-Alder reaction support a concerted mechanism for the parent triyne (1,3,8-nonatriyne); however, a slight electronic advantage in the concerted path may be outweighed by the difference in entropy of activation for sequential vs simultaneous formation of two new ring bonds.
authors.affiliation: Department of Chemistry and Materials Science Program, University of New Hampshire , Durham, New Hampshire 03824, United States.|Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Skraba-Joiner
authors.affiliation: Department of Chemistry and Materials Science Program, University of New Hampshire , Durham, New Hampshire 03824, United States.|Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Johnson
authors.affiliation: Department of Chemistry and Materials Science Program, University of New Hampshire , Durham, New Hampshire 03824, United States.|Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Jay
authors.initials: J
authors.lastname: Agarwal