E/Z product distribution in the metathesis of allyl alcohol derivatives with a first generation ruthenium-based catalyst

2011 ◽  
Vol 52 (31) ◽  
pp. 3992-3994 ◽  
Author(s):  
Jonathan R. Moulins ◽  
D. Jean Burnell
Keyword(s):  
Allyl Alcohol ◽  
First Generation ◽  
Product Distribution

The Evans Synthesis of (–)-Nakadomarin A

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Synthesis ◽  
Allyl Alcohol ◽  
First Generation ◽  
Direct Conversion ◽  
Heck Coupling ◽  
Ring Closing Metathesis ◽  
Selective Activation ◽  
Enantiomerically Pure ◽  
Ru Catalyst ◽  
Nakadomarin A

(–)-Nakadomarin A (4), isolated from the marine sponge Amphimedon sp. off the coast of Okinawa, shows interesting cytotoxic and antibacterial activity. David A. Evans of Harvard University prepared (J. Am. Chem. Soc. 2013, 135, 9338) 4 by coupling the enantiomerically pure lactam 2 with the prochiral lactam 1. The preparation of 1 began with the aldehyde 5. Following the Comins protocol, addition of lithio morpholine to the carbonyl gave an intermediate that could be metalated and iodinated. Protection of the aldehyde followed by Heck coupling with allyl alcohol gave the aldehyde 7. Addition of the phosphorane derived from 8 followed by deprotection gave 9 with the expected Z selectivity. Addition of the phosphonate 10 was also Z selective, leading to the lactam 1. The preparation of 2 began with the enantiomerically pure imine 12. The addition of 13 was highly diastereoselective, setting the absolute configuration of 15. Alkylation with the iodide 16 delivered 17, which was closed to 2 under conditions of kinetic ring-closing metathesis, using the Grubbs first generation Ru catalyst. The condensation of 1 with 2 gave both of the diastereomeric products, with a 9:1 preference for the desired 3. Experimentally, acid catalysis alone did not effect cyclization, suggesting that the cyclization is proceeding via silylated intermediates. The diastereoselectivity can be rationalized by a preferred extended transition state for the intramolecular Michael addition. Selective activation of 3 followed by reduction gave 18, which underwent Bischler-Napieralski cyclization to give an intermediate that could be reduced to (–)-nakadomarin A (4). It was later found that exposure of 3 to Tf2O and 19 followed by the addition of Redal gave direct conversion to 4. It is instructive to compare this work to the two previous syntheses of 4 that we have highlighted, by Dixon (OHL May 3, 2010) and by Funk (OHL July 4, 2011). Together, these three independent approaches to 4 showcase the variety and dexterity of current organic synthesis.

Experimental and reaction kinetic investigation of 1-octene metathesis reaction with Hoveyda-Grubbs first generation precatalyst

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Percy van der Gryp ◽  
Sanette Marx ◽  
Hermanus C.M. Vosloo
Keyword(s):  
Reaction Temperature ◽  
First Generation ◽  
Reaction System ◽  
Reaction Rates ◽  
Product Distribution ◽  
Molar Ratio ◽  
Distribution Data ◽  
Metathesis Reaction ◽  
Pseudo First Order Reaction ◽  
Catalyst Load

Abstract In this work, we report the catalytic performance of the first generation Hoveyda-Grubbs precatalyst for the metathesis reaction of 1-octene. The reaction temperature (30 to 100°C) and catalyst load (1-octene/Ru molar ratio 5,000 to 10,000) were varied and quantities such as product distribution, activity and selectivity were evaluated. Reaction temperature showed a significant effect and turn over numbers as high as 4458 were observed for this system. Two competing mechanisms were observed for temperatures above 60°C, namely metathesis and isomerisation. The experimental product-time distribution data for the complex parallel reaction system was fairly accurately described by three elementary pseudo-first order reaction rates. The effects of temperature (Arrhenius Equation) and catalyst load were incorporated in the observed rate constant. The observed activation energies were around 10 kcal/mol.

scholarly journals Multi-generation chemical aging of <i>α</i>-pinene ozonolysis products by reactions with OH

2018 ◽  
Vol 18 (5) ◽  
pp. 3589-3601 ◽  
Author(s):  
Ningxin Wang ◽  
Evangelia Kostenidou ◽  
Neil M. Donahue ◽  
Spyros N. Pandis
Keyword(s):  
Hydroxyl Radicals ◽  
Atomic Oxygen ◽  
First Generation ◽  
Organic Aerosol ◽  
Product Distribution ◽  
Smog Chamber ◽  
Experimental Conditions ◽  
Chemical Aging ◽  
Significant Difference ◽  
Volatile Organic

Abstract. Secondary organic aerosol (SOA) formation from volatile organic compounds (VOCs) in the atmosphere can be thought of as a succession of oxidation steps. The production of later-generation SOA via continued oxidation of the first-generation products is defined as chemical aging. This study investigates aging in the α-pinene ozonolysis system with hydroxyl radicals (OH) through smog chamber experiments. The first-generation α-pinene ozonolysis products were allowed to react further with OH formed via HONO photolysis. After an equivalent of 2–4 days of typical atmospheric oxidation conditions, homogeneous OH oxidation of the α-pinene ozonolysis products resulted in a 20–40 % net increase in the SOA for the experimental conditions used in this work. A more oxygenated product distribution was observed after aging based on the increase in aerosol atomic oxygen-to-carbon ratio (O : C) by up to 0.04. Experiments performed at intermediate relative humidity (RH) of 50 % showed no significant difference in additional SOA formation during aging compared to those performed at a low RH of less than 20 %.

scholarly journals The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene

2021 ◽  
Author(s):  
Philip T. M. Carlsson ◽  
Luc Vereecken ◽  
Anna Novelli ◽  
François Bernard ◽  
Birger Bohn ◽  
...  
Keyword(s):  
Gas Phase ◽  
First Generation ◽  
Product Distribution ◽  
Chem Phys ◽  
Oxidation Products ◽  
Rate Coefficients ◽  
Peroxy Radicals ◽  
Model Calculations ◽  
Alkoxy Radicals ◽  
Wide Range

&lt;p&gt;Experiments at atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the reaction of isoprene with NO&lt;sub&gt;3&lt;/sub&gt; and its subsequent oxidation. Due to the production of NO&lt;sub&gt;3&lt;/sub&gt; from the reaction of NO&lt;sub&gt;2&lt;/sub&gt; with O&lt;sub&gt;3&lt;/sub&gt; as well as the formation of OH in subsequent reactions, the reactions of isoprene with O&lt;sub&gt;3&lt;/sub&gt; and OH were estimated to contribute up to 15% of the total isoprene consumption each in these experiments. The ratio of RO&lt;sub&gt;2&lt;/sub&gt; to HO&lt;sub&gt;2&lt;/sub&gt; concentrations was varied by changing the reactant concentrations, which modifies the product distribution from bimolecular reactions of the nitrated RO&lt;sub&gt;2&lt;/sub&gt;. The reaction with HO&lt;sub&gt;2&lt;/sub&gt; or NO&lt;sub&gt;3&lt;/sub&gt; was found to be the main bimolecular loss process for the RO&lt;sub&gt;2&lt;/sub&gt; radicals under all conditions examined.&lt;/p&gt;&lt;p&gt;Yields of the first-generation isoprene oxygenated nitrates as well as the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) were determined by high resolution proton mass spectrometry using the Vocus PTR-TOF. The experimental time series of these products are compared to model calculations based on the MCM v3.3.1,&lt;sup&gt;1&lt;/sup&gt; the isoprene mechanism as published by Wennberg &lt;em&gt;et al.&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; and the newly developed FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism,&lt;sup&gt;3&lt;/sup&gt; which incorporates theory-based rate coefficients for a wide range of reactions.&lt;/p&gt;&lt;p&gt;Among other changes, the FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism contains a novel fast oxidation route through the epoxidation of alkoxy radicals, originating from the formation of nitrated peroxy radicals. This inhibits the formation of MVK and MACR from the NO&lt;sub&gt;3&lt;/sub&gt;-initiated oxidation of isoprene to practically zero, which agrees with the observations from chamber experiments. In addition, the FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism increases the level of agreement for the main first-generation oxygenated nitrates.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; M. E. Jenkin, J. C. Young and A. R. Rickard, The MCM v3.3.1 degradation scheme for isoprene, &lt;em&gt;Atmospheric Chem. Phys.&lt;/em&gt;, 2015, &lt;strong&gt;15&lt;/strong&gt;, 11433&amp;#8211;11459.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&lt;/sup&gt; P. O. Wennberg &lt;em&gt;at al.&lt;/em&gt;, Gas-Phase Reactions of Isoprene and Its Major Oxidation Products, &lt;em&gt;Chem. Rev.&lt;/em&gt;, 2018, &lt;strong&gt;118&lt;/strong&gt;, 3337&amp;#8211;3390.&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3&lt;/sup&gt; L. Vereecken &lt;em&gt;et al.&lt;/em&gt;, Theoretical and experimental study of peroxy and alkoxy radicals in the NO3-initiated oxidation of isoprene, &lt;em&gt;Phys. Chem. Chem. Phys.&lt;/em&gt;, submitted.&lt;/p&gt;

scholarly journals Multi-generation Chemical Aging of α-Pinene Ozonolysis Products by Reactions with OH

2017 ◽  
Author(s):  
Ningxin Wang ◽  
Evangelia Kostenidou ◽  
Neil M. Donahue ◽  
Spyros N. Pandis
Keyword(s):  
Hydroxyl Radicals ◽  
Atomic Oxygen ◽  
First Generation ◽  
Organic Aerosol ◽  
Product Distribution ◽  
Smog Chamber ◽  
Experimental Conditions ◽  
Chemical Aging ◽  
Significant Difference ◽  
Volatile Organic

Abstract. Secondary organic aerosol (SOA) formation from volatile organic compounds (VOCs) in the atmosphere can be thought of as a succession of oxidation steps. The production of later-generation SOA via continued oxidation of the first-generation products is defined as chemical aging. This study investigates aging in the α-pinene ozonolysis system with hydroxyl radicals (OH) through smog chamber experiments. The first-generation α-pinene ozonolysis products were allowed to react further with OH formed via HONO photolysis. After an equivalent of 2–4 days' of typical atmospheric oxidation conditions, homogeneous OH oxidation of the α-pinene ozonolysis products resulted in a 20–40 % net increase of the SOA for the experimental conditions used in this work. A more oxygenated product distribution was observed after aging based on the increase in aerosol atomic oxygen to carbon ratio (O : C) by up to 0.04. Experiments performed at intermediate relative humidity (RH) of 50 % showed no significant difference in additional SOA formation during aging compared to those performed at low RH of less than 20 %.

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