Corner versus Edge Protonation of Cyclopropane

Abstract

Acid-catalyzed addition of methanol to 1 occurs by rupture of the internal carbon-carbon bond of the cyclopropane to give 2 with both retention and inversion at the site of electrophilic attack (4:5, 1.3:1.0). Nucleophilic attack occurs with inversion without relaxation of the corner-and edgeprotonated cyclopropanes to a secondary cation.

Application of the Cplex-isoelectronic theory to electrocyclisations, sigmatropic rearrangements, cheletropic reactions and antiaromaticityConsistent with Santilli's hadronic chemistry

“…The carbon of the cyclopropane ring that is attacked by the nucleophile always occurs with inversion as in S N 2 reactions and the pertinent carbon centre of the cyclopropane ring that reacts with the proton (electrophile) can occur with either inversion or retention with inversion usually favoured. This pathway also occurs without skeletal rearrangement, consistent with a one step pathway [5]. Inversion occurs in the 2 process of the dipolar [3 + 2] cycloaddition [1].…”

“…The Cplex-isoelectronic theory is consistent with the experimental data and makes different predictions from the present quantum chemical methods in some cases, namely a stepwise pathway for the conrotatory photochemical ring opening of 1,3-cyclohexadiene, a concerted photochemical electrocyclisation for 1,3-cyclohexadiene via disrotatory motion, a concerted suprafacial [1,5] sigmatropic shift with inversion for norcaradiene, a concerted suprafacial [1,3] carbon shift with inversion and retention, a concerted suprafacial photochemical [1,5] hydrogen migration, a concerted photochemical [3,3] shift, stabilisation of cyclic 4n electron systems by delocalisation and their excess energy is due only to electronic repulsion and strain, the monohomocyclopropenium and cyclopropenyl cations are not 'aromatic'. The available empirical evidence is consistent with these new predictions.…”

“…reaction for the [1,5] H migration of (S)-cis,trans-3-methyl-7-deutero-octa-4,6-diene under thermal conditions consistent with a concerted process and the ADEP prediction [29]. The single bond breaks in the 1 process as opposed to the double bonds as it ensures the subsequent weaker bonds can be broken (Section 2.1).…”

“…The ADEP assumption predicts a suprafacial process for the [1,5] H sigmatropic shift as illustrated by 14 in Fig. 7.…”

“…Inversion can occur in all the subsequent processes, because the decrease in electron density is triggered and neutralised by the incoming electron density from the previous process. Literature precedence for this concept can be found in the reaction of the cyclopropane ring with nucleophiles under acid catalysis [5]. The carbon of the cyclopropane ring that is attacked by the nucleophile always occurs with inversion as in S N 2 reactions and the pertinent carbon centre of the cyclopropane ring that reacts with the proton (electrophile) can occur with either inversion or retention with inversion usually favoured.…”