The Chemistry of Laurenene. XVI. Investigation of the Mechanism of a Cationic Rearrangement

1993 ◽  
Vol 46 (8) ◽  
pp. 1163 ◽  
Author(s):  
DB Clarke ◽  
RT Weavers
Keyword(s):  
Rearrangement Product ◽  
Deuterium Label ◽  
Deuterium Labelling ◽  
Hydride Shift ◽  
Product Composition ◽  
Cationic Rearrangement

Some aspects of the mechanism of the acid-induced rearrangement of laurenan-2β-ol have been deduced from deuterium- labelling studies. A key intermediate arises from two pathways, one involving a 1,4- and one a 1,5-hydride shift. Formation of this intermediate is partially suppressed by substitution of the migrating hydrogen by a deuterium. A proposed pathway which involves a 1,3-methyl migration has been disproved, and scrambling and loss of deuterium label has been accounted for in terms of equilibria involving lauren-1-ene and another previously reported rearrangement product. The rearrangement is strongly promoted in dichloromethane, and the product composition is highly solvent-dependent.

Acetolytic cleavage of 2β,19-Epoxy-5α-cholestane involving a 1,2-Hydride shift to C2

1977 ◽  
Vol 30 (10) ◽  
pp. 2249 ◽  
Author(s):  
RE Gall ◽  
J Taylor
Keyword(s):  
Acetic Anhydride ◽  
Boron Trifluoride ◽  
Shift Reagent ◽  
Deuterium Exchange ◽  
Paramagnetic Shift ◽  
Nucleophilic Attack ◽  
Rearrangement Product ◽  
Hydride Shift ◽  
Carbonium Ion

Acetolytic cleavage of 2β,19-epoxy-5α-cholestane (1a) with boron trifluoride and acetic anhydride followed by hydrolysis gave the 2α,19- diol (2b), the only rearrangement product the 1α,19-diol (3b) and a mixture of olefins (4b). Deuterium exchange studies and the use of a paramagnetic shift reagent have shown that the reaction leading to the rearranged diol(3b) is not concerted and appears to involve an intermediate carbonium ion since hydride shift from both C 1 and C 3 occur. The formation of the 1α,19-diol (3b) as the only rearranged product can be rationalized as nucleophilic attack on the acetoxonium ion (8).

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. III. Generation and Rearrangement of Aryloxycarbenes by Intramolecular Abstraction of Hydrogen

1979 ◽  
Vol 32 (1) ◽  
pp. 111 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Gas Phase ◽  
Hydrogen Abstraction ◽  
Low Pressure ◽  
Insertion Reactions ◽  
Vinyl Ethers ◽  
Deuterium Labelling ◽  
Hydride Shift

o-Alkoxy- and o-alkylthio-phenylcarbenes, generated by low-pressure pyrolysis in the gas phase, show abstraction of 2H across space to generate the corresponding o-tolyl vinyl ethers or sulfides. In the case of o-ethoxyphenylcarbene, deuterium labelling shows that this is a case of vicinal abstraction, not geminal abstraction followed by 1,2-hydride shift. o-Methoxyphenylcarbene, however, is similarly shown to undergo geminal hydrogen abstraction leading to o-tolyloxycarbene, which undergoes a 1,2-aryl shift to give o-tolualdehyde. Independent generation of aryloxycarbenes has been achieved by pyrolysis of 5-aryloxy-2,2-dimethyl-l,3-dioxan- 4,6-diones. The product carbenes show the expected rearrangement as well as normal insertion reactions.

Bromination of Norbornene: the Question of Bromonium Ions vs. 6,1-Hydride Shift

1971 ◽  
Vol 49 (6) ◽  
pp. 885-903 ◽  
Author(s):  
D. R. Marshall ◽  
P. Reynolds-Warnhoff ◽  
E. W. Warnhoff ◽  
J. R. Robinson
Keyword(s):  
Carbon Tetrachloride ◽  
Complex Mixture ◽  
Radical Mechanism ◽  
Hydride Shift ◽  
Product Composition ◽  
Kinetically Controlled ◽  
Ionic Addition ◽  
Made In

The reaction of norbornene (1) with bromine has been re-investigated and found to give in addition to bromonortricyclene (2) and 2-exo-bromonorbornane (20) a complex mixture of dibromides of which five (15–19) have been isolated and identified. These dibromides have been found to be kinetically controlled products of ionic addition. Apparently dibromide 15 is also formed to some extent in carbon tetrachloride by a radical mechanism. The product composition from the bromine addition has been compared with that of the analogous chlorination and bromofluorination reactions. Degradation of the 2-exo,3-endo-dibromonorbornane from bromination of 5,6-14C-norbornene has shown that this dibromide is formed by two ionic routes: (a) from a bromonium ion 14 (or its equivalent), and (b) from the cation 12 formed by 6,1-hydride shift. Improvements have been made in the first and final steps of the standard norbornene degradation method.

Reaction of 1,4-dibromohexafluoro-2-butene with O- and N-nucleophiles

1988 ◽  
Vol 53 (3) ◽  
pp. 619-625 ◽  
Author(s):  
Ivan Hemer ◽  
Věra Moravcová ◽  
Václav Dědek
Keyword(s):  
Kinetic Study ◽  
Sodium Methoxide ◽  
Allylic Rearrangement ◽  
Rearrangement Product

Reaction of 1,4-dibromohexafluoro-2-butene (I) with sodium methoxide, ethoxide or isopropoxide in the corresponding alcohols proceeds with allylic rearrangement under formation of 3-alkoxy-4-bromohexafluoro-1-butenes II-IV. A kinetic study has proven the SN2’ mechanism for reaction of I with potassium phenoxide leading to 4-bromo-3-phenoxyhexafluoro-1-butene (V). Also the reaction of I with ammonia, affording 3-amino-4-bromo-2,4,4-trifluoro-2-butenenitrile (IX), is compatible with the allylic rearrangement by SN2’ mechanism. On the contrary, reaction of I with diethylamine gave no rearrangement product and, after hydrolysis, afforded N,N-diethyl-4-bromo-2,3,3,4,4-pentafluorobutanamide (XVI) and N,N-diethyl-4-bromo-2,3,4,4-tetrafluoro-2-butenamide (XVII) in the ratio 85:15.

Selectivity changes of acetone transformation over ZSM-5 zeolites with different acido-basic properties

1989 ◽  
Vol 54 (8) ◽  
pp. 2054-2063 ◽  
Author(s):  
Jiří Čejka ◽  
Ludmila Kubelková ◽  
Pavel Jírů
Keyword(s):  
Main Product ◽  
High Conversion ◽  
Total Conversion ◽  
Basic Properties ◽  
Product Composition ◽  
Conversion Level ◽  
Integral Reactor ◽  
Low Activity ◽  
High Conversion Level

Acetone transformation catalyzed by HZSM-5 and NaZSM-5 zeolites and by zeolites modified with basic oxides was studied in an integral reactor at a temperature of 350 °C. Modification of acido-basic properties of ZSM-5 zeolites resulted both in the total conversion changes and in the essential changes in the product composition. Isobutene was found to be the main product over HZSM-5 zeolites exhibiting low activity, while aromatics prevailed when high conversion level was attained. Classical condensation of acetone yielding mesityloxide and phorones was observed over NaZSM-5 zeolites impregnated with CaO and ZnO.

scholarly journals Regioselective activation of benzocyclobutenones and dienamides lead to anti-Bredt bridged-ring systems by a [4+4] cycloaddition

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jianyu Zhang ◽  
Xi Wang ◽  
Tao Xu
Keyword(s):  
Type Ii ◽  
Ring Systems ◽  
Hydride Shift

AbstractTo the best of our knowledge, bridgehead carbon benzofused-bridged ring systems have previously not been accessible to the synthetic community. Here, we describe a formal type-II [4 + 4] cycloaddition approach that provides fully sp2-carbon embedded anti-Bredt bicyclo[5.3.1] skeletons through the Rh-catalyzed C1–C8 activation of benzocyclobutenones (BCBs) and their coupling with pedant dienamides. Variously substituted dienamides have been coupled with BCBs to provide a range of complex bicyclo[5.3.1] scaffolds (>20 examples, up to 89% yield). The bridged rings were further converted to polyfused hydroquinoline-containing tetracycles via a serendipitously discovered transannular 1,5-hydride shift/Prins-like cyclization/Schmidt rearrangement cascade.

scholarly journals Rendering Fat and Heavy Fischer-Tropsch Waxes Mixtures (0–100%) Fast Pyrolysis Tests for the Production of Ethylene and Propylene

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 367
Author(s):  
Martyna Murat ◽  
Zahra Gholami ◽  
Josef Šimek ◽  
Daily Rodríguez-Padrón ◽  
José Miguel Hidalgo-Herrador
Keyword(s):  
Linear Chain ◽  
High Energy ◽  
Chain Structure ◽  
Nitrogen Atmosphere ◽  
Energy Materials ◽  
Fischer Tropsch ◽  
Pyrolysis Products ◽  
Product Composition ◽  
Rendered Fat ◽  
Linear Chain Structure

A great emphasis is placed on searching for efficient sources to produce renewable fuels due to the actual trends in avoiding the use of fossil resources to mitigate the environment’s deterioration. Thus, the use of waste from the food or wood industry for the production of biofuels is widely researched and may contribute to sustainable general development. Rendered fat and Fischer-Tropsch waxes are high-energy materials which could be used for the pyrolysis reaction. Therefore, in this study, the effect of reaction parameters and feedstock composition on the distribution of the pyrolysis products has been examined. The experiments were carried out in a nitrogen atmosphere in a multi-shot pyrolizer instrument equipped with GC-FID. First, the influence of the temperature was examined at 785, 800, and 815 °C. The highest yield to olefins was observed at 815 °C. The effect of triglycerides and paraffins contents (0–100% with 10% ramp) in the feedstock on the product composition was investigated at 815 °C. The gas chromatography analyses revealed that the feedstock composition did not significantly affect the product composition due to the high temperature and the long linear chain structure similarities between the free fatty acids and Fischer-Tropsch waxes.

Estimation of groundwater recharge via deuterium labelling in the semi-arid Cuvelai-Etosha Basin, Namibia

2015 ◽  
Vol 51 (4) ◽  
pp. 533-552 ◽  
Author(s):  
Matthias Beyer ◽  
Marcel Gaj ◽  
Josefina Tulimeveva Hamutoko ◽  
Paul Koeniger ◽  
Heike Wanke ◽  
...  
Keyword(s):  
Groundwater Recharge ◽  
Deuterium Labelling ◽  
Semi Arid
Sign in / Sign up

Export Citation Format

Share Document