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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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.v3 ◽

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

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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Fe(III)-Activated Sulfite Revisited: The Overlooked Role of High-Valent Iron(IV)-Oxo Complex (Fe(IV)) in Water Treatment

10.21203/rs.3.rs-724195/v1 ◽

2021 ◽

Author(s):

Luna Luo ◽

Zhen Wang ◽

Qin Guo ◽

Xipeng Wei ◽

Jianpeng Hu ◽

...

Keyword(s):

Free Radicals ◽

Kinetic Model ◽

Chemical Properties ◽

Relative Contribution ◽

Phenyl Sulfone ◽

High Valent ◽

Hydrolysis Of ◽

Methyl Phenyl

Abstract Sulfate radical (SO4•−) and its secondary radical (hydroxyl radical, •OH) are commonly recognized as the primary reactive intermediates formed by Fe(III)/sulfite system. However, it still remains unknown whether Fe(IV) is involved in this system where the well documented Fe(IV)-precursors (i.e., Fe(II) and persulfates) were in-situ generated. Intriguingly, we observed that methyl phenyl sulfone (PMSO2), indicative of Fe(IV) formation, was formed during methyl phenyl sulfoxide (PMSO) transformation in Fe(III)/sulfite system, which unprecedently verified that Fe(IV) played a crucial role in it. In parallel, the involvement of SO4•− and •OH in this system were also identified, but the limited •OH was proposed to be derived from hydrolysis of both Fe(IV) and SO4•−, rather than by self-decay of SO4•− alone. Moreover, the contribution of Fe(IV) relative to it of free radicals was explored by monitoring the yield of PMSO2. It was disclosed that the relative contribution of Fe(IV) was progressively promoted as Fe(III)-sulfite reaction proceeding with an upper limit of 80%-90%, and it was accelerated by promoting Fe(III) and sulfite dosages, while was declined with increasing pH. Furthermore, a kinetic model was developed, which precisely simulated kinetic traces of PMSO transformation and dissolved oxygen evolution in Fe(III)/sulfite system. More importantly, the kinetic model offered the first insight into the evolution of Fe(IV), SO4•−, and •OH, which provided in-depth mechanistic understanding of the iron-catalyzed sulfite auto-oxidation process. Considering the different chemical properties between Fe(IV) and free radicals, it is urgent to re-evaluate the decontamination process by iron/sulfite system.

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Mechanistic Studies of Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification

10.26434/chemrxiv.13693540.v1 ◽

2021 ◽

Author(s):

Yuxuan Ye ◽

Seoung-Tae Kim ◽

Ryan P. King ◽

Mu-Hyun Baik ◽

Stephen L. Buchwald

Keyword(s):

Trans Isomer ◽

Computational Study ◽

Reductive Elimination ◽

Nucleophilic Attack ◽

Ligand Modification ◽

Low Efficiency ◽

Vinyl Triflates ◽

Nucleophilic Fluorination

<div><div><div>Pd-catalyzed nucleophilic fluorination reactions are important methods for the synthesis of fluoroarenes and fluoroalkenes. However, these reactions can generate a mixture of regioisomeric products that are often difficult to separate. While investigating the Pd- catalyzed fluorination of cyclic vinyl triflates, we observed that the addition of a substoichiometric quantity of TESCF3 significantly improves both the efficiency and the regioselectivity of the fluorination process. Herein, we report a combined experimental and computational study on the mechanism of this transformation focused on the role of TESCF3. We found that in the absence of additives such as TESCF3, the transmetalation step produces predominantly the thermodynamically more stable trans isomer of the key LPd(vinyl)F complex (L = biaryl monophosphine ligand). This intermediate, rather than undergoing reductive elimination, preferentially reacts through an intramolecular β-deprotonation to form a Pd-cyclohexyne intermediate. This undesired reactivity is responsible for the low efficiency (11% yield) and poor regioselectivity (1.8:1) of the catalytic reaction. When TESCF3 is added to the reaction mixture, the cis-LPd(vinyl)F complex is instead formed, through a pathway involving an unusual dearomatization of the ligand by nucleophilic attack from a trifluoromethyl anion (CF3–). In contrast to the trans isomer, this cis-LPd(vinyl)F complex readily undergoes reductive elimination to provide the vinyl fluoride product with desired regioselectivity, without the generation of Pd-cyclohexyne intermediates.</div></div></div>

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Mechanistic Studies of Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification

10.26434/chemrxiv.13693540 ◽

2021 ◽

Author(s):

Yuxuan Ye ◽

Seoung-Tae Kim ◽

Ryan P. King ◽

Mu-Hyun Baik ◽

Stephen L. Buchwald

Keyword(s):

Trans Isomer ◽

Computational Study ◽

Reductive Elimination ◽

Nucleophilic Attack ◽

Ligand Modification ◽

Low Efficiency ◽

Vinyl Triflates ◽

Nucleophilic Fluorination

<div><div><div>Pd-catalyzed nucleophilic fluorination reactions are important methods for the synthesis of fluoroarenes and fluoroalkenes. However, these reactions can generate a mixture of regioisomeric products that are often difficult to separate. While investigating the Pd- catalyzed fluorination of cyclic vinyl triflates, we observed that the addition of a substoichiometric quantity of TESCF3 significantly improves both the efficiency and the regioselectivity of the fluorination process. Herein, we report a combined experimental and computational study on the mechanism of this transformation focused on the role of TESCF3. We found that in the absence of additives such as TESCF3, the transmetalation step produces predominantly the thermodynamically more stable trans isomer of the key LPd(vinyl)F complex (L = biaryl monophosphine ligand). This intermediate, rather than undergoing reductive elimination, preferentially reacts through an intramolecular β-deprotonation to form a Pd-cyclohexyne intermediate. This undesired reactivity is responsible for the low efficiency (11% yield) and poor regioselectivity (1.8:1) of the catalytic reaction. When TESCF3 is added to the reaction mixture, the cis-LPd(vinyl)F complex is instead formed, through a pathway involving an unusual dearomatization of the ligand by nucleophilic attack from a trifluoromethyl anion (CF3–). In contrast to the trans isomer, this cis-LPd(vinyl)F complex readily undergoes reductive elimination to provide the vinyl fluoride product with desired regioselectivity, without the generation of Pd-cyclohexyne intermediates.</div></div></div>

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A Short, Efficient, and Stereoselective Synthesis of Piperine and its Analogues

Synlett ◽

10.1055/s-0037-1611652 ◽

2019 ◽

Vol 30 (04) ◽

pp. 413-416 ◽

Cited By ~ 1

Author(s):

Adriano Bauer ◽

Jun-Hyun Nam ◽

Nuno Maulide

Keyword(s):

Ring Opening ◽

Stereoselective Synthesis ◽

Starting Material ◽

Nucleophilic Attack ◽

Wide Range ◽

Quantitative Synthesis ◽

Pentadienoic Acid

A quantitative synthesis of piperine from commercially available starting material is presented. The synthesis relies on a stereoselective nucleophilic attack of an in situ generated cuprate onto a cyclobutene lactone. The so-formed aryl-substituted cyclobutene spontaneously undergoes a conrotatory 4π-electrocyclic ring opening to form the 4-aryl pentadienoic acid as a single diastereoisomer. The high-yielding synthesis can be easily modulated on the aryl and on the amide moiety for the synthesis of a wide range of piperine analogues.

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Cu(I)-Catalyzed Synthesis of β,γ-Unsaturated Amides

Synlett ◽

10.1055/s-0036-1589135 ◽

2017 ◽

Vol 29 (04) ◽

pp. 463-466

Author(s):

André Isaacs ◽

Aaron Bosse ◽

Gregory Tsougranis ◽

Christopher DeTroia ◽

Francisco Tejidor

Keyword(s):

Ring Opening ◽

Nucleophilic Attack ◽

Mild Conditions ◽

Propargyl Alcohols

Readily available propargyl alcohols were found to be useful substrates for the copper(I)-catalyzed synthesis of β,γ-unsaturated amides. Nucleophilic attack by the alcohol on the in situ generated ketenimine followed by base-catalyzed elimination and subsequent ring opening yields the desired products under mild conditions.

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