Permethyl-4,4′-bis-Δ1,2-pyrazolinylibene () the synthesis and x-ray chystallographic structure of a highly crowded olefin

Bushby, Richard J.; Pollard, Michael D.; McDonald, Walter S.

doi:10.1016/s0040-4039(01)95078-6

Cited by 19 publications

(3 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In particular, the structures of 4-methylenepyrazolines having no such hindrance are of interest on the considering the mechanism of the decomposition of the alkyl-idenepyrazolines 14 , the structures of which have been so far reported on only two derivatives. 4-Isopropylidene-3,3,5,5-tetramethylpyrazoline-1 40 does not adopt a folded envelope structure but an almost planar one, whereas methylenepyrazoline 41 has a folded structure with the dihedral angle 16° . Both compounds are, however, not suitable to confirm whether 14 adopts inherently a planar or an envelope structure, because the more the ring is folded the greater becomes the steric crash between the methyl groups on C-3 and C-5, suggesting that presence of these methyl groups flattens the ring.…”

Section: Discussionmentioning

confidence: 99%

“…4-Isopropylidene-3,3,5,5-tetramethylpyrazoline-1 40 does not adopt a folded envelope structure but an almost planar one, 20 whereas methylenepyrazoline 41 has a folded structure with the dihedral angle 16°. 21 Both compounds are, however, not suitable to confirm whether 14 adopts inherently a planar or an envelope structure, because the more the ring is folded the greater becomes the steric crash between the methyl groups on C-3 and C-5, suggesting that presence of these methyl groups flattens the ring. Therefore, to confirm the inherent structure of normal alkylidenepyrazolines, we have performed the X-ray crystal analysis of 14a with small steric interaction between the substituents on C-3 and hydrogens on C-5 as a typical model of normal 4-alkylidenepyrazolines.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition

et al. 2003

View full text Add to dashboard Cite

Thermal decomposition of 4-alkylidenepyrazolines 14 bearing a methoxycarbonyl group at C-3, prepared by 1,3-dipolar cycloaddition between allenecarboxylates 12 and diazoalkanes 13, was carried out. Unlike normal 4-alkylidenepyrazolines, which decompose in stepwise mechanisms at high temperatures, 14 decomposed concertedly at moderately low temperatures (45-110 degrees C), resulting in selective formation of the two isomeric alkylidenecyclopropanes 7 arising from the bond formation between the exo-methylene carbon and the 5-carbon. The selective formation and the configurations of the products are rationalized in terms of the concerted process via the folded conformation of the pyrazolines. Introduction of an electron-withdrawing group at the 3-position of the 4-alkylidenepyrazoline system causes the polarization of the C(3)-N(2) bond inducing the properties of intramolecular diazonium salt 8, in which the pi-electrons on the methylene carbon become more nucleophilic and participate in the cleavage of the C(5)-N(1) bond. The X-ray crystal structure of the typical normal alkylidenepyrazoline 14a with only small steric interactions between the substituents was determined to be a nearly planar ring structure.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition

et al. 2003

View full text Add to dashboard Cite

show abstract

“…Attempted Preparation of Bi-3,3,5,5-Tetramethylthiacyclohexylidene (7). Compounds 13 (75 mg, 0.32 mmol) and 14 (63 mg, 0.34 mmol) in dry tetrahydrofuran (0.5 mL) under dry nitrogen were stirred for 3 days, and then the mixture was heated to reflux for 6 days.…”

Section: Methodsmentioning

confidence: 99%

Multiple extrusion methods for the preparation of sterically hindered olefins. An approach to tetra-tert-butylethylene

Guziec¹,

Murphy²

1980

J. Org. Chem.

View full text Add to dashboard Cite

Twofold Extrusion Reactions

Guziec

2012

Organic Reactions

View full text Add to dashboard Cite

Twofold extrusion reactions are chemical transformations in which two small inorganic molecules or atoms connecting carbon or nitrogen atoms are lost, generating the corresponding carbon‐carbon or carbon‐nitrogen double bonds. These reactions are particularly useful for the preparation of sterically hindered alkenes and imines. The inorganic species liberated in twofold extrusion reactions can be molecular nitrogen, sulfur, selenium, tellurium, sulfur dioxide, sulfur monoxide, carbon dioxide or carbon monoxide. The most common precursors for twofold extrusion reactions are 1,3,4‐thiadiazolines, which thermally extrude molecular nitrogen affording thiiranes. These thiiranes can be readily desulfurized to afford the corresponding alkenes using tertiary phosphines. The corresponding 1,3,4‐selenadiazolines thermally extrude both molecular nitrogen and atomic selenium directly affording alkenes. Alkenes can also be prepared by formal extrusions of molecular nitrogen plus sulfur dioxide or sulfur monoxide. Extremely sterically hindered imines can be prepared by extrusions of molecular nitrogen and sulfur or selenium from in situ generated heterocyclic precursors. Other less common twofold extrusion reactions are also reported. The detailed preparations of the required precursors for the twofold extrusion reactions as well as the mechanisms of these extrusion processes are discussed in this chapter. The utility of twofold extrusion reactions in the preparations of ‘molecular rotors’ and other extremely sterically hindered alkenes is presented. The steric limitations of the twofold extrusion reactions are discussed along with comparisons of these reactions with other alkene‐ and imine‐forming synthetic methods. The Tabular Survey covers material through the end of 2009.

show abstract

Permethyl-4,4′-bis-Δ1,2-pyrazolinylibene () the synthesis and x-ray chystallographic structure of a highly crowded olefin

Cited by 19 publications

References 15 publications

Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition

Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition

Multiple extrusion methods for the preparation of sterically hindered olefins. An approach to tetra-tert-butylethylene

Twofold Extrusion Reactions

Contact Info

Product

Resources

About