Synthetic Applications of Intramolecular Insertion in Arylcarbenes. II. o-Alkoxy-, Dialkylamino- and Alkylthio-phenylcarbenes

1979 ◽  
Vol 32 (1) ◽  
pp. 99 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Membered Ring ◽  
Ring Formation ◽  
High Yield ◽  
Side Chains ◽  
Ortho Position ◽  
Carbene Insertion ◽  
Donor Capacity

A series of phenylcarbenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.20mm. Carbene insertion occurs in moderate to high yield to give the appropriate five-and six-membered heterocyclics, the former predominating. The regioselectivity of the carbene insertion (five-membered ring us six-membered ring) is highest in the case of the alkoxy and dialkylamino compounds, where six-membered-ring formation is relatively minor; in the case of the alkylthiophenylcarbenes, the selectivity in favour of the smaller ring is, by comparison, small. The reasons for this are discussed in terms of the geometry of the transition state and the donor capacity of the heteroatom.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. IV. o-Alkoxy-, Dialkylamino- and Alkylthio-1-phenylethylidenes

1979 ◽  
Vol 32 (1) ◽  
pp. 123 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Side Chains ◽  
Ortho Position ◽  
No Formation ◽  
Carbene Insertion ◽  
Transition State Geometry

A series of 1-phenylethylidenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.30 mm. Carbene insertion to form five-membered heterocyclic rings predominates, with up to 20% Bamford-Stevens insertion, to give the styrenes; little or no formation of six-membered rings is observed. In cases where stereoselective insertion is possible, the trans-disubstituted heterocycle is formed preferentially, the selectivity being greatest in the case of dialkylamino substitution. The mechanisms involved are discussed in terms of transition state geometry.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. I. o-Alkylphenylcarbenes and 1-(o-Alkylphenyl)ethylidenes

1979 ◽  
Vol 32 (1) ◽  
pp. 89 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Hydrogen Atom ◽  
Gas Phase ◽  
Chain Length ◽  
Membered Ring ◽  
Ring Formation ◽  
Ortho Position ◽  
Methyl Group ◽  
Alkyl Chains ◽  
Out Of Plane

A series of phenylcarbenes and 1-phenylethylidenes, substituted in the ortho-position by alkyl chains of 1-4 carbon atoms, has been generated in the gas phase and pyrolysed at 250-750°/0.05-0.10 mm. Apart from o-tolylcarbene, the phenylcarbenes show efficient insertion to form five- and six-membered rings, the former predominating. In the phenylethylidenes, Bamford-Stevens insertion into the adjacent methyl group competes with cyclization to an extent which decreases with chain length. At the same time, five-membered ring formation is greatly increased over six-membered ring formation, due to facilitation of out-of-plane twisting of the carbene atom. The mechanistic implications of the results are discussed in terms of an angular approach of the carbene p-orbital to the hydrogen atom under attack.

scholarly journals Theoretical Inversion of Amino Acids (Alanine and Aspartic Acid) by Semi-Empirical Methods

2013 ◽  
Vol 12 ◽  
pp. 37-44
Author(s):  
Musa E. Mohamed
Keyword(s):  
Activation Energy ◽  
Amino Acids ◽  
Transition State ◽  
Gas Phase ◽  
Aspartic Acid ◽  
Aqueous Phase ◽  
Free Amino ◽  
Membered Ring ◽  
Empirical Methods ◽  
Semi Empirical

The inversion reaction coordinate of free amino acids (alanine, aspartic acid) have been computationally calculated by semi-empirical methods AM1. A transition state for free alanine and aspartic acid were obtained as a three membered ring in which the α-C-H and α-C-CH3 are slightly elongated, 1.2 and 2.17 Å respectively in the alanine transition state. The activation energy of alanine is 77.52 kcal/mol in the gas phase and 76.66 kcal/mol in aqueous phase, and for aspartic acid is 54.87 kcal/mol in the gas phase and 50.86 kcal/mol in aqueous phase.

An Alternate Energy-Conserved Pathway for the Morita-Baylis-Hillman (MBH) Reaction

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Lower Energy ◽  
Aldol Reaction ◽  
Membered Ring ◽  
Ammonium Ion ◽  
Alternate Energy ◽  
Ring Transition State ◽  
Mbh Reaction

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann<i> </i>elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

An Alternate Energy-Conserved Pathway for the Morita-Baylis-Hillman (MBH) Reaction

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Lower Energy ◽  
Aldol Reaction ◽  
Membered Ring ◽  
Ammonium Ion ◽  
Alternate Energy ◽  
Ring Transition State ◽  
Mbh Reaction

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann<i> </i>elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

Electron-Transfer-Induced Side-Chain Cleavage in Tryptophan Facilitated through Potassium-Induced Transition-State Stabilization in the Gas Phase

2021 ◽  
Author(s):  
Filipe Ferreira da Silva ◽  
Tiago Cunha ◽  
Andre Rebelo ◽  
Adrià Gil ◽  
Maria José Calhorda ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transition State ◽  
Gas Phase ◽  
Side Chain ◽  
Side Chain Cleavage ◽  
Transition State Stabilization ◽  
Chain Cleavage

Molecular orbital structures of sulfones

1982 ◽  
Vol 60 (6) ◽  
pp. 730-734 ◽  
Author(s):  
Russell J. Boyd ◽  
Jeffrey P. Szabo
Keyword(s):  
Crystal Structure ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Comparison With Experiment ◽  
The Difference

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.

Ring formation via β-keto ester dianions

1977 ◽  
Vol 55 (6) ◽  
pp. 996-1000 ◽  
Author(s):  
Phaik-Eng Sum ◽  
Larry Weiler
Keyword(s):  
Membered Ring ◽  
Ring Formation ◽  
Methyl Acetoacetate ◽  
Keto Ester ◽  
Keto Esters

The reaction of α,ω-dihalides with the dianion of methyl acetoacetate gives a mixture of mono- and bisalkylated products. The monoalkylated products can be cyclized via the monoanion to cyclic β-keto esters with a seven- or eight-membered ring. Alternatively these monoalkylated products can be cyclized via the dianion to γ-cyclopentyl- or γ-cyclohexyl-β-keto esters.

Five vs Six Membered-Ring PAH Products from Reaction of o-Methylphenyl Radical and two C3H4 Isomers

2021 ◽  
Author(s):  
Oisin J Shiels ◽  
Matthew Brian Prendergast ◽  
John Savee ◽  
David L Osborn ◽  
Craig A. Taatjes ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Membered Ring ◽  
Gas Phase Reactions

Gas-phase reactions of the o-methylphenyl (o-CH3C6H4) radical with the C3H4 isomers allene (H2C=C=CH2) and propyne (HCºC-CH3) are studied at 600 K and 4 Torr (533 Pa) using VUV synchrotron photoionisation mass spectrometry,...

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