Woodward-Hoffmann rules: Cycloaddition reactions

Abstract

Woodward-Hoffmann Rules:Cycloaddition Reactions A major innovation in organic chemistry has been the development of a set of symmetry-based selection rules for concerted chemical reactions (1). These rules, named Woodward-Hoffmann rules in honor of their authors, have proved to be a powerful tool for predicting the preferred pathway and stereochemical course of certain reactions. In a recent review article in this Journal we have attempted to elucidate the derivation and application of the Woodward-Hoffmann rules for electro cyclic reactions (2). Another -class of reactions which can be understood in a similar maimer are those called cycloaddition reactions (i3). A few examples in this reaction class are (4-9)The preceding reactions are called cycloaddition reactions because they occur with ring formation between two conjugated ir-eleetron systems, involving

The reactivity of cyclopropyl cyanide in titan's atmosphere: a possible pre-biotic mechanism

“…The study was done at the CASSCF level being able to describe the full singlet electronic wave function of the system including contributions from open-shell singlet configurations. Results shown the reaction behaves as a pericyclic cycloaddition reaction 52,53,54,57 . From the experimental mass spectra shown in Figure 2, the ratio of signal intensities at m/z 135 (product adduct ion) and m/z 68 (parent ion signal) can be obtained at different nominal laboratory collision energies (CE) corresponding to 1.0, 2.0, 4.0 and 6.0 eV.…”

“…4). In the other direction it leads to another minimum associated with a new cyclic product showing a five-center ring due to the formation of two new covalent bonds involving C(12)≡N(11), C1 and C3 atoms, as in the case of a [2+2] pericyclic cycloaddition reaction 52,53,54 . The structure of the most stable conformer (P1) is shown in Figure 10, while internal and dihedral angles in P1 are given in Table 5.…”

Structure-resonance theory for pericyclic transition states

“…The Cope rearrangement, and the Claisen reaction are often cited (20)(21)(22)(23) as examples of pericyclic six electron [3,3] sigmatropic shifts.…”

Ketene cycloadditions

“…If more than one pericyciic reaction (26)(27)(28)(29)(30)(31)(32) is possible for a ketene then the stereochemical variable of perispecificity must he studied; i.e., which process is selected by the ketene and what is the quantitative preference for that process. For example, a ketene is allowed by the considerations of orbital symmetry (26) to cycloadd to 1,3-cyclopentadiene (acting as the ketenophile) in either a (ir2 + tt4) or a (ir2 + ?r2) manner.…”