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

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

10.26434/chemrxiv.7791146.v4 ◽

2021 ◽

Author(s):

Veejendra Yadav ◽

Dasari L V K Prasad ◽

Arpita Yadav ◽

Maddali L N Rao

Keyword(s):

Lewis Acid ◽

Ring Opening ◽

Reaction Pathway ◽

Chloride Ion ◽

Thermodynamic Control ◽

Heterolytic Cleavage ◽

Acid Catalyzed ◽

Halogen Acid

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans-trans-1,1,3-tris-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the sC3C4 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-tris-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the sC3C4 bond to allow its heterolytic SN2 cleavage by the chloride ion. This is followed by cisoid→transoid 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-tris-carbethoxycyclobutene in CH2Cl2, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the sC3C4 bond. The resultant species subsequently undergoes cisoid→transoid isomerization before losing the Lewis acid to form the products.

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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

10.26434/chemrxiv.7791146 ◽

2020 ◽

Author(s):

Veejendra Yadav ◽

Dasari L V K Prasad ◽

Arpita Yadav ◽

Maddali L N Rao

Keyword(s):

Lewis Acid ◽

Ring Opening ◽

Chloride Ion ◽

Thermodynamic Control ◽

Heterolytic Cleavage ◽

Acid Catalyzed ◽

Halogen Acid

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans-trans-1,1,3-tris-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the sC3C4 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-tris-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the sC3C4 bond to allow its heterolytic SN2 cleavage by the chloride ion. This is followed by cisoid→transoid 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-tris-carbethoxycyclobutene in CH2Cl2, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the sC3C4 bond. The resultant species subsequently undergoes cisoid→transoid isomerization before losing the Lewis acid to form the products.

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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

10.26434/chemrxiv.7791146.v5 ◽

2021 ◽

Author(s):

Veejendra Yadav ◽

Dasari L V K Prasad ◽

Arpita Yadav ◽

Maddali L N Rao

Keyword(s):

Lewis Acid ◽

Ring Opening ◽

Reaction Pathway ◽

Chloride Ion ◽

Ester Group ◽

Heterolytic Cleavage ◽

Acid Catalyzed ◽

Halogen Acid

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans,trans-1,1,3-tris-carbethoxy-4-methyl- and s-trans,trans-1,1,3-tris-carbethoxy-4-phenyl-1,3-butadienes, respectively, are discussed to proceed through pathways entailing heterolytic cleavage of the sC3C4 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 sC3C4 bond and allow its SN2 cleavage by chloride ion. This is followed by cisoid→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-tris-carbethoxycyclobutene in CH2Cl2, coordination of Lewis acid with the geminal ester group is followed by heterolytic cleavage of the sC3C4 bond. The resultant species subsequently undergoes cisoid→transoid isomerization before losing the Lewis acid to form the products.

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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

10.26434/chemrxiv.7791146.v1 ◽

2019 ◽

Author(s):

Veejendra Yadav ◽

Dasari L V K Prasad ◽

Arpita Yadav ◽

Maddali L N Rao

Keyword(s):

Ring Opening ◽

Nucleophilic Attack ◽

Thermodynamic Control ◽

Heterolytic Cleavage ◽

Methyl Phenyl ◽

Halogen Acid

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans-trans-1,1,3-tris-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through a pathway entailing heterolytic cleavage of sC3C4 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 sC3C4 bond to allow its heterolytic cleavage and formation of a stable cation or protonation followed by halide ion attack in SN2 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 SN2 cleavage of sC3C4 bond is also discussed.

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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

10.26434/chemrxiv.7791146.v2 ◽

2020 ◽

Author(s):

Veejendra Yadav ◽

Dasari L V K Prasad ◽

Arpita Yadav ◽

Maddali L N Rao

Keyword(s):

Ring Opening ◽

Nucleophilic Attack ◽

Thermodynamic Control ◽

Heterolytic Cleavage ◽

Methyl Phenyl ◽

Halogen Acid

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans-trans-1,1,3-tris-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through a pathway entailing heterolytic cleavage of sC3C4 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 sC3C4 bond to allow its heterolytic cleavage and formation of a stable cation or protonation followed by halide ion attack in SN2 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 SN2 cleavage of sC3C4 bond is also discussed.

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Catalytic Carbonyl-Olefin Metathesis of Aliphatic Ketones: Iron(III) HomoDimers as Lewis Acidic Superelectrophiles

10.26434/chemrxiv.7130801.v1 ◽

2018 ◽

Author(s):

Haley Albright ◽

Paul S. Riehl ◽

Christopher C. McAtee ◽

Jolene P. Reid ◽

Jacob R. Ludwig ◽

...

Keyword(s):

Lewis Acid ◽

Olefin Metathesis ◽

Acid Activation ◽

Lewis Acid Catalysts ◽

Distinct Mode ◽

Aliphatic Ketones ◽

Carbon Carbon Bond ◽

Metathesis Reactions ◽

Acid Catalyzed

<div>Catalytic carbonyl-olefin metathesis reactions have recently been developed as a powerful tool for carbon-carbon bond</div><div>formation. However, currently available synthetic protocols rely exclusively on aryl ketone substrates while the corresponding aliphatic analogs remain elusive. We herein report the development of Lewis acid-catalyzed carbonyl-olefin ring-closing metathesis reactions for aliphatic ketones. Mechanistic investigations are consistent with a distinct mode of activation relying on the in situ formation of a homobimetallic singly-bridged iron(III)-dimer as the active catalytic species. These “superelectrophiles” function as more powerful Lewis acid catalysts that form upon association of individual iron(III)-monomers. While this mode of Lewis acid activation has previously been postulated to exist, it has not yet been applied in a catalytic setting. The insights presented are expected to enable further advancement in Lewis acid catalysis by building upon the activation principle of “superelectrophiles” and broaden the current scope of catalytic carbonyl-olefin metathesis reactions.</div>

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