Borohydride reduction of .sigma.-bonded organopalladium complexes in the norbornenyl-nortricyclenyl system. Evidence against a radical mechanism

1970 ◽  
Vol 92 (23) ◽  
pp. 6965-6967 ◽  
Author(s):  
Edwin. Vedejs ◽  
Mary F. Salomon
Keyword(s):  
Radical Mechanism ◽  
Borohydride Reduction

Hydrostibination of Alkynes: A Radical Mechanism

2020 ◽  
Author(s):  
Josh MacMillan ◽  
Katherine Marczenko ◽  
Erin Johnson ◽  
Saurabh Chitnis
Keyword(s):  
Density Functional ◽  
Activation Barrier ◽  
Closed Shell ◽  
Reaction Rates ◽  
Radical Mechanism ◽  
Neutral Radical ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Ionic Mechanisms ◽  
Terminal Acetylenes

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov <i>Z</i>-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical Sb<sup>II</sup> and Sb<sup>III</sup> intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol<sup>-1</sup> of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb<sup>II</sup> and Sb<sup>III</sup> intermediates to yield the observed <i>Z</i>-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as <i>E</i>-olefins.

Regioselective C3-H Trifluoromethylation of 2H-Indazole Under Transition-Metal-Free Photoredox Catalysis

2019 ◽  
Author(s):  
Arumugavel Murugan ◽  
Venkata Nagarjuna Babu ◽  
Nagaraj Sabarinathan ◽  
Sharada Duddu. S
Keyword(s):  
Transition Metal ◽  
Visible Light ◽  
Practical Approach ◽  
Hypervalent Iodine ◽  
Radical Mechanism ◽  
Photoredox Catalysis ◽  
Metal Free

Here we report a visible-light-promoted metal-free regioselective C3-H trifluoromehtylation reaction that proceeds via radical mechanism and which supported by control experiments. The combination of photoredox catalysis and hypervalent iodine reagent provides a practical approach for the present trifluoromethylation reaction and synthesis of a library of trifluoromethylated indazoles.

Synthesis of (15E)-17β-hydroxy-5α-androstane-3,15-dione 15-[O-(Carboxymethyl)]oxime, New Hapten for Dihydrotestosterone (17β-hydroxy-5α-androstan-3-one)

1997 ◽  
Vol 62 (10) ◽  
pp. 1642-1649 ◽  
Author(s):  
Ivan Černý ◽  
Tereza Slavíková ◽  
Vladimír Pouzar
Keyword(s):  
Hydroxy Group ◽  
Carboxy Group ◽  
Title Compound ◽  
Oxidative Cleavage ◽  
Hydroxy Derivative ◽  
Borohydride Reduction ◽  
Protecting Group ◽  
Free Hydroxy Group

Addition of 4-methoxybenzyl alcohol to 3β-hydroxy-5α-androst-15-en-17-one gave the mixture of isomeric 15-(4-methoxyphenyl)methoxy derivatives from which, after acetylation and chromatography, the major 15β isomer was separated. Borohydride reduction gave 17β-hydroxy derivative which was protected as methoxymethyl ether. Oxidative cleavage of protecting group at position 15 and the subsequent Jones oxidation afforded corresponding 15-ketone. Its oximation with O-(carboxymethyl)hydroxylamine, deacetylation and methylation with diazomethane gave protected O-(carboxymethyl)oxime derivative with free hydroxy group at position 3. Its oxidation afforded dihydrotestosterone derivative and successive deprotection of position 17 and of carboxy group led to final (15E)-17β-hydroxy-5α-androstane-3,15-dione 15-[O-(carboxymethyl)]oxime. The title compound was designed as dihydrotestosterone hapten for heterologous radioimmunoassays.

Sterically Crowded Heterocycles. VII. Reduction of Some (Z)-1,3-Diphenyl-3-(2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2-en-1-ones as Their Axial Chirality Probe

1996 ◽  
Vol 61 (7) ◽  
pp. 1018-1026 ◽  
Author(s):  
Richard Kubík ◽  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Hydroxy Derivative ◽  
Borohydride Reduction ◽  
Axial Chirality ◽  
Pm3 Calculations

Borohydride reduction of titled ketones 1a-1g gave diastereoisomeric mixtures of (Z)-1,3-diphenyl-3-(2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2-en-1-ols 2a-2g and 3a-3g in which the former ones prevailed. Only individual racemic products were obtained after borohydride reduction of (E)-1,3-diphenyl-3-(2-phenylimidazo[1,2-a]pyridin-3-yl)-prop-2-en-1-one 4 to corresponding 1-hydroxy derivative 5 and by conversion of (Z)-1-oxo derivative 1a to 1,3-diphenyl-3-(2-phenylimidazo[1,2-a]pyridin-3-yl)propan-1-one (6) with sodium hydrogenselenide. Diastereoselectivity of the borohydride reduction is discussed using the PM3 calculations of the molecules 1a, 2a, 2b, 3a, 3b, 4, 5, and 6.

ChemInform Abstract: PYRIDAZINES. LXXXIV. STUDIES ON BOROHYDRIDE REDUCTION OF PYRIDAZINE COMPOUNDS

1976 ◽  
Vol 7 (52) ◽  
pp. no-no
Author(s):  
P. K. KADABA ◽  
B. STANOVNIK ◽  
M. TISLER
Keyword(s):  
Borohydride Reduction

Comparative QSAR evidence for a free-radical mechanism of phenol-induced toxicity

2000 ◽  
Vol 127 (1) ◽  
pp. 61-72 ◽  
Author(s):  
Corwin Hansch ◽  
Susan C. McKarns ◽  
Carr J. Smith ◽  
David J. Doolittle
Keyword(s):  
Free Radical ◽  
Radical Mechanism ◽  
Free Radical Mechanism
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