Thermolysis of unsymmetrically substituted vinylcyclopropanes. The effect of substituents on the site-selectivity of homo-[1,5]-sigmatropic hydrogen migrations

1984 ◽  
Vol 62 (11) ◽  
pp. 2392-2395 ◽  
Author(s):  
Edward Piers ◽  
Anderson Richard Maxwell
Keyword(s):  
Substituent Effect ◽  
Sharp Contrast ◽  
Effect Of Substituents ◽  
Site Selectivity ◽  
Hydrogen Shifts

Thermolysis of the unsymmetrical vinylcyclopropanes 18–24 reveals a notable substituent effect on the site-selectivity of homo-[1,5]-sigmatropic hydrogen shifts. Rearrangement of 18–20 (OMe substituent) produces only products 25–27, respectively (HA migration). In sharp contrast, thermolysis of 24 (Me3Si substituent) provides exclusively substance 34 (HX migration). Thermolysis of substrates bearing methyl (21, 22) or phenyl (23) groups provide, in each case, mixtures of the two possible products.

Effect of substituents on absorption and fluorescence properties of pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines

2008 ◽  
Vol 86 (11) ◽  
pp. 1070-1076 ◽  
Author(s):  
Bhausaheb K Ghotekar ◽  
Muddassar A Kazi ◽  
Madhukar N Jachak ◽  
Raghunath B Toche
Keyword(s):  
Good Yield ◽  
Substituent Effect ◽  
Photophysical Properties ◽  
Fluorescence Properties ◽  
Absorption And Emission ◽  
Effect Of Substituents ◽  
Convenient Route

A convenient route was successfully developed for the synthesis of novel heterocycles such as pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines (PPP) from pyrazolo[3,4-b]pyridines in good yield. The PPP derivatives synthesized were further studied for their photophysical properties, and it was observed that absorption and emission λmax changed, owing to the substituent effect at 4 positions. These compounds were obtained from highly reactive starting materials, 5-aminopyrazoles and α-acetyl γ-butyrolactone.Key words: α-acetyl γ-butyrolactone, pyrazolo[3,4-b]pyrrolo[2,3-d] pyridine, absorption, emission, fluorescence.

Substituent effect studies on the thermal [1,5]-sigmatropic hydrogen shifts of vinylallenes

1987 ◽  
Vol 109 (24) ◽  
pp. 7499-7506 ◽  
Author(s):  
Giin Yuan Shen ◽  
Ricardo Tapia ◽  
William H. Okamura
Keyword(s):  
Substituent Effect ◽  
Hydrogen Shifts

Substituent effect on fluorescence signaling of the cell permeable HSO4− receptors through single point to ratiometric response in green solvent

RSC Advances ◽  
2014 ◽  
Vol 4 (53) ◽  
pp. 27665-27673 ◽  
Author(s):  
Manjira Mukherjee ◽  
Siddhartha Pal ◽  
Buddhadeb Sen ◽  
Somenath Lohar ◽  
Samya Banerjee ◽  
...  
Keyword(s):  
Substituent Effect ◽  
Single Point ◽  
Green Solvent ◽  
Effect Of Substituents ◽  
Biological Studies ◽  
Fluorescence Signaling

Effect of substituents on tuning of fluorescence signaling of the cell permeable HSO4− ions receptors through single point to ratiometric response in green solvent was systematically explored through analytical and biological studies.

Chelation-assisted transition metal-catalysed C–H chalcogenylations

2020 ◽  
Vol 7 (8) ◽  
pp. 1022-1060 ◽  
Author(s):  
Wenbo Ma ◽  
Nikolaos Kaplaneris ◽  
Xinyue Fang ◽  
Linghui Gu ◽  
Ruhuai Mei ◽  
...  
Keyword(s):  
Transition Metal ◽  
Recent Advances ◽  
Site Selectivity ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

This review summarizes recent advances in C–S and C–Se formations via transition metal-catalyzed C–H functionalization utilizing directing groups to control the site-selectivity.

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

Imine as a Linchpin Approach for Distal C(sp2)–H Functionalization

2020 ◽  
Author(s):  
Sukdev Bag ◽  
Sadhan Jana ◽  
Sukumar Pradhan ◽  
Suman Bhowmick ◽  
Nupur Goswami ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Bond Activation ◽  
Bond Formation ◽  
Ancillary Ligand ◽  
Significant Challenge ◽  
Site Selectivity ◽  
Directing Group ◽  
Covalently Linked ◽  
Complex Organic ◽  
Post Functionalization

<p>Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing group (DG) served as an ancillary ligand to ensure proximal <i>ortho</i>-, distal <i>meta</i>- and <i>para</i>-C-H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. We introduce here a transient directing group for distal C(<i>sp<sup>2</sup></i>)-H functionalization <i>via</i> reversible imine formation. By overruling facile proximal C-H bond activation by imine-<i>N</i> atom, a suitably designed pyrimidine-based transient directing group (TDG) successfully delivered selective distal C-C bond formation. Application of this transient directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the distal position has been explored.</p>

Theoretical and experimental studies of palladium-catalyzed site-selective C(sp3)−H bond functionalization enabled by transient ligands

2017 ◽  
Author(s):  
Haibo Ge ◽  
Lei Pan ◽  
Piaoping Tang ◽  
Ke Yang ◽  
Mian Wang ◽  
...  
Keyword(s):  
Bond Activation ◽  
Theoretical Calculations ◽  
Experimental Studies ◽  
Bond Functionalization ◽  
Aliphatic Ketones ◽  
Site Selectivity ◽  
Mechanistic Investigation ◽  
Palladium Catalyzed ◽  
Metal Catalyzed ◽  
Site Selective

Transition metal-catalyzed selective C–H bond functionalization enabled by transient ligands has become an extremely attractive topic due to its economical and greener characteristics. However, catalytic pathways of this reaction process on unactivated sp<sup>3</sup> carbons of reactants have not been well studied yet. Herein, detailed mechanistic investigation on Pd-catalyzed C(sp<sup>3</sup>)–H bond activation with amino acids as transient ligands has been systematically conducted. The theoretical calculations showed that higher angle distortion of C(sp2)-H bond over C(sp3)-H bond and stronger nucleophilicity of benzylic anion over its aromatic counterpart, leading to higher reactivity of corresponding C(sp<sup>3</sup>)–H bonds; the angle strain of the directing rings of key intermediates determines the site-selectivity of aliphatic ketone substrates; replacement of glycine with β-alanine as the transient ligand can decrease the angle tension of the directing rings. Synthetic experiments have confirmed that β-alanine is indeed a more efficient transient ligand for arylation of β-secondary carbons of linear aliphatic ketones than its glycine counterpart.<br><br>

The Gender Troubles of Feofan Prokopovich

2020 ◽  
Vol 54 (1-3) ◽  
pp. 198-228
Author(s):  
Gary Marker
Keyword(s):  
Sharp Contrast ◽  
Close Reading ◽  
Dual Codes ◽  
Minimalist Approach ◽  
Holy Women ◽  
Gender Trouble

Abstract This essay constitutes a close reading of the works of Feofan Prokopovich that touch upon gender and womanhood. Interpretively it is informed by Judith Butler’s book Gender Trouble, specifically by her model of gender-as-performance. Prokopovich’s writings conveyed a negative characterization of holy women and Russian women of power, a combination of glaring silences and Scholastic dual codes that in toto denied the association of womanhood with glory or wisdom. In this he stood apart from other East Slavic Orthodox homilists of his day, even though they too invariably associated virtue with masculinity (muzhestvo). For Prokopovich, wisdom, strength, constancy, etc., were innately masculine. Women, by contrast, were weak, inconstant, non-rational, and guided by emotion. His sermons nominally in praise of Catherine I and Anna Ioannovna were suffused with narrative gestures that, to those attuned to the nuances of Scholastic rhetoric, ran entirely counter to their nominal message. Several panegyrics to Anna, for example, made no mention of her at all, a practice in sharp contrast to his sermons to male rulers, which typically placed the honoree firmly in the foreground. Even more startling is his singularly minimalist approach to Mary, for whom he composed almost no sermons and whose presence he barely mentioned in tracts where one would have expected otherwise. This essay concludes that this attitude reflected both his personal preferences and influence that Protestant Pietism had on his thinking.

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