On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity. An alternate reaction pathway

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>,<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and s-<i>trans</i>,<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-phenyl-1,3-butadienes, respectively, are discussed to proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction by protonation of the geminal ester group to weaken s_C3C4 bond and allow its S_N2 cleavage by chloride ion. This is followed by cisoid<b>→</b>transoid isomerization and loss of the elements of halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of Lewis acid with the geminal ester group is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes cisoid<b>→</b>transoid isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity. An alternate reaction pathway

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through a pathway entailing heterolytic cleavage of s_C3C4 bond rather than the usual four-electron conrotatory ring opening. The adventitious or in situ generated halogen acid catalyzes the reaction by either protonation of one of the two ester groups on C3 and, thus, weakening s_C3C4 bond to allow its heterolytic cleavage and formation of a stable cation or protonation followed by halide ion attack in S_N2 manner on the methyl/phenyl-bearing carbon. Reorganization of the cation species formed in the former event and elimination of the elements of halogen acid from the halo-species formed in the latter event generate the observed product. The nucleophilic attack of DMSO to bring about heterolytic S_N2 cleavage of s_C3C4 bond is also discussed.</p>

ab initio Method on the Mechanism of Acetalization of 2-Methoxybenzaldehyde Using Halogen Acid Catalysts

ab initio method used on the mechanism of acetalization of 2-methoxybenzaldehyde. ab initio method is a quantum mechanical approximate calculation and derived directly only from theoretical principles. All geometry optimizations were performed using 3-21G and 6-31G* basis set with Hyperchem 8.0 software (windows version). The aim of this study was to focus on the study of the mechanism of acetalization of 2-methoxybenzaldehyde using hydrochloric acid as catalysts. The computational calculation not only provided possible reaction steps but also provided possible energy change in each step of the reaction mechanism of acetalization of 2-methoxybenzaldehyde. The result showed that 2-methoxybenzaldehyde (0 kJ/mol) has the lowest energy and electronegativity compared to acetal product (-17.43 kJ/mol) and a labile hemiacetal (448.33 kJ/mol) due to its stability and the influence of neighbour atom.

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through a pathway entailing heterolytic cleavage of s_C3C4 bond rather than the usual four-electron conrotatory ring opening. The adventitious or in situ generated halogen acid catalyzes the reaction by either protonation of one of the two ester groups on C3 and, thus, weakening s_C3C4 bond to allow its heterolytic cleavage and formation of a stable cation or protonation followed by halide ion attack in S_N2 manner on the methyl/phenyl-bearing carbon. Reorganization of the cation species formed in the former event and elimination of the elements of halogen acid from the halo-species formed in the latter event generate the observed product. The nucleophilic attack of DMSO to bring about heterolytic S_N2 cleavage of s_C3C4 bond is also discussed.</p>