The orbital-symmetry rules of Hoffman-Woodward allow thermal combination between 2π+2σ electrons of vinyl-cyclopropane and 2π-cyclophiles such as tetracyanoethylene (TCNE), N-chlorosulfenylisocyanate (CSI), 4-phenyl-1,2,4-triazoline-3.5-dione (PTAD), maleic anhydride (MA), and dimethylacetylene dicarboxylate (DMAD), to form the respective seven-membered rings by way of [5+2] cycloaddition.  Because of analogy to dienes, vinylcyclopropanes were labeled “homodienes”, and their cycloreaction with 2π-cyclophiles in the [5+2] manner as Homo-Diels-Alder Reaction, or “homodiene synthesis”.  Homo-Diels-Alder reactions (leading to cycloheptenes)  were shown to depend on three factors.  First, the energy factor, express- ed in terms of energy difference between the ionization potentials (IP) of the vinylcyclopropane (electron donor substrate) and the electron affinity (EA) of the 2π-cyclophile (electron acceptor) {Δ(IP-EA) eV),  requiring Δ(IP-EA) to exceed 5 eV.  Secondly, the steric factor, demanding that the p-orbital axis of the vinyl group and the plane of the three-membered ring assume antiperiplanar (s-trans) conformation.  Thirdly, the mechanistic factor, expecting adherence to pericyclic rules (orbital symmetry rules).  [2+2] Mode of assembly may compete effectively with [5+2] cyclo- addtion when Δ(IP-EA) becomes less than 4-5 eV.

According to their mode of cycloaddition, the 2π-cyclophiles are grouped into four types: 1) of EA » 3 eV (TCNE, DDQ, TCNQ); 2) of EA » 2 eV (PTAD); 3) EA > 1 eV (CSI); 4) of EA » 0.5 eV (DMAD, MA).  The substrates are grouped according to their conformational constellations.  They comprise a wide range of both sterically constrained and non-constrained homodienes such as: divinylcyclopropane, bicyclic systems related to [x. 1. 0] alkenes, monospiromethyl-ene-, and momospirocyclopropylidene-cycloalkanes, dispiro-1 methylenecycloalkanemethylene-, and alkylidenecyclopropanes, homofulvene, unsaturated propellane tricyclo[5.3.1.0]undeca-2,4,9-triene, benzvalene, divinylcyclopropanes, butadienylidenespiroalkanes, substituted butadienylcyclopropane and dicyclopropylethylenes.

Sterically constrained divinylcyclopropanes combine with common, electron-deficient 2π-cycloaddends in three distinctly different ways, i.e., [7+2], [5+2], and [2+2], depending on substrate structure, of the particular partner and the reaction conditions.

Transition-metals provide powerful catalysts for cyclo additons by two distinct categories: 1) intermolecular, and 2) intra-molecular.  Thus, Fe(CO)₅ catalyzes intermolecular [5+1] and [7+1] carbonylative cyclo additions to vinyl-, and divinylcyclopropanes.  IrCl(CO)(PPh₃)₃ and Co₂(CO)₈ catalyze [5+1] carbonylative cycloaddtions to allenylcyclopropanes.

RhCl(PPh₃)₃ catalyzes intramolecular [5+2] cycloaddtions of vinylcyclopropane and alkynes.  Vinyl-, allenyl-, divinyl-, and butadienyl-cyclopropanes are shown to provide new building-blocks for constructing common, medium and large carbocycles and heterocylces by a variety of modes of cycloaddition.