Økt mestringstro og motivasjon hos masterstudenter

Det finnes i dag mange studier for oppfølging og veiledning av ph.d.-studenter, men tilsvarende få for master-gradsstudenter, til tross for at den store majoriteten av studenter avslutter utdanningen med nettopp mastergraden.Kartlegging viste at mange studenter er usikre på sin egen rolle i arbeidet med masteroppgaven. I tillegg har mangelav motivasjon og mestringstro. Vi har sett på hvordan veiledning og rammer kan gjøres bedre med små og enkle grep,blant annet ved å oppmuntre studentene til å jobbe med laboratoriearbeid, teori og skriving parallelt. De viktigstetiltakene som ble gjennomført, er aktiv bruk av læringsplattformen, bedre opplæring innen litteratursøk og merøvelse i muntlig og skriftlig formidling. Resultatene viser at studentene ble mer drevet av indre motivasjon, følermer eierskap og har økt mestringstro etter at tiltakene ble innført.publishedVersio

Atmospheric Chemistry of tert-butylamine and AMP

The atmospheric chemistry of (CH3)3CNH2 (tert-butylamine, tBA) and (CH3)2(CH2OH)CNH2 (2-amino-2-methyl-1-propanol, AMP) has been studied by quantum chemistry methods and in photo-oxidation experiments in the EUPHORE chamber in Valencia (Spain). Aerosol formation and composition has been quantified. Yields of nitramines and other products in the photo-oxidations have been determined and complete photo-oxidation schemes including branching between the major reaction routes have been obtained. Published by Elsevier Ltd

Atmospheric Chemistry of 2-Amino-2-methyl-1-propanol : A Theoretical and Experimental Study of the OH-Initiated Degradation under Simulated Atmospheric Conditions

The OH-initiated degradation of 2-amino-2-methyl-1-propanol [CH3C(NH2)(CH3)CH2OH, AMP] was investigated in a large atmospheric simulation chamber, employing time-resolved online high-resolution proton-transfer reaction-time-of-flight mass spectrometry (PTR-ToF-MS) and chemical analysis of aerosol online PTR-ToF-MS (CHARON-PTR-ToF-MS) instrumentation, and by theoretical calculations based on M06-2X/aug-cc-pVTZ quantum chemistry results and master equation modeling of the pivotal reaction steps. The quantum chemistry calculations reproduce the experimental rate coefficient of the AMP + OH reaction, aligning k(T) = 5.2 × 10-12 × exp (505/T) cm3 molecule-1 s-1 to the experimental value kexp,300K = 2.8 × 10-11 cm3 molecule-1 s-1. The theoretical calculations predict that the AMP + OH reaction proceeds via hydrogen abstraction from the -CH3 groups (5-10%), -CH2- group, (>70%) and -NH2 group (5-20%), whereas hydrogen abstraction from the -OH group can be disregarded under atmospheric conditions. A detailed mechanism for atmospheric AMP degradation was obtained as part of the theoretical study. The photo-oxidation experiments show 2-amino-2-methylpropanal [CH3C(NH2)(CH3)CHO] as the major gas-phase product and propan-2-imine [(CH3)2C=NH], 2-iminopropanol [(CH3)(CH2OH)C=NH], acetamide [CH3C(O)NH2], formaldehyde (CH2O), and nitramine 2-methyl-2-(nitroamino)-1-propanol [AMPNO2, CH3C(CH3)(NHNO2)CH2OH] as minor primary products; there is no experimental evidence of nitrosamine formation. The branching in the initial H abstraction by OH radicals was derived in analyses of the temporal gas-phase product profiles to be BCH3/BCH2/BNH2 = 6:70:24. Secondary photo-oxidation products and products resulting from particle and surface processing of the primary gas-phase products were also observed and quantified. All the photo-oxidation experiments were accompanied by extensive particle formation that was initiated by the reaction of AMP with nitric acid and that mainly consisted of this salt. Minor amounts of the gas-phase photo-oxidation products, including AMPNO2, were detected in the particles by CHARON-PTR-ToF-MS and GC×GC-NCD. Volatility measurements of laboratory-generated AMP nitrate nanoparticles gave ΔvapH = 80 ± 16 kJ mol-1 and an estimated vapor pressure of (1.3 ± 0.3) × 10-5 Pa at 298 K. The atmospheric chemistry of AMP is evaluated and a validated chemistry model for implementation in dispersion models is presented

Theoretical and Experimental Study on the Reaction of tert-Butylamine with OH Radicals in the Atmosphere

The OH-initiated atmospheric degradation of tert-butylamine (tBA), (CH3)3CNH2, was investigated in a detailed quantum chemistry study and in laboratory experiments at the European Photoreactor (EUPHORE) in Spain. The reaction was found to mainly proceed via hydrogen abstraction from the amino group, which in the presence of nitrogen oxides (NOx), generates tert-butylnitramine, (CH3)3CNHNO2, and acetone as the main reaction products. Acetone is formed via the reaction of tert-butylnitrosamine, (CH3)3CNHNO, and/or its isomer tert-butylhydroxydiazene, (CH3)3CN=NOH, with OH radicals, which yield nitrous oxide (N2O) and the (CH3)3Ċ radical. The latter is converted to acetone and formaldehyde. Minor predicted and observed reaction products include formaldehyde, 2-methylpropene, acetamide and propan-2-imine. The reaction in the EUPHORE chamber was accompanied by strong particle formation which was induced by an acid-base reaction between photochemically formed nitric acid and the reagent amine. The tert-butylaminium nitrate salt was found to be of low volatility, with a vapor pressure of 5.1 × 10-6 Pa at 298 K. The rate of reaction between tert-butylamine and OH radicals was measured to be 8.4 (±1.7) × 10-12 cm3 molecule-1 s-1 at 305 ± 2 K and 1015 ± 1 hPa

Totalsyntese som et verktøy for strukturoppklaring av noen marine naturprodukter med lipid struktur

Paper I describes the total synthesis of the proposed structure of mucosin, a C20 fatty acid, isolated from a Mediterranean sponge, Reniera mucosa. The synthetic pathway started with the transformation of 1,4-cyclohexadiene to a known meso-ketone in three steps. Employing a chiral base, an optically active β-keto ester, also previously described in literature, was obtained in excellent stereochemical purity. In a thirteen-step linear sequence, including a copper mediated cross-coupling, onepot alumination/halodemetallation/Negishi cross-coupling protocol, gave the proposed structure of (-)-mucosin. Comparison of spectral data with the literature reported values revealed discrepancies. By employing X-ray crystallography on a late stage intermediate, it was demonstrated that the relative stereochemistry assigned to mucosin had been achieved. This also proved that the structure claimed in literature is most likely incorrect. Paper II describes the total synthesis of the diastereomer of the proposed structure of mucosin. Taking advantage of the same keto ester from paper I, we prepared an α,β-unsaturated ester enabling an inverted motive for the conjugate addition. By this strategy we made the anti-diastereomer of the proposed structure for mucosin. This demonstrated that the natural product most likely does not contain a cis-fused bicyclic core, since the prepared material did not match the reported data. Paper III describes the synthesis of crucigasterin 277, a sphingolipid isolated from the Mediterranean tunicate, Pseudomonas crucigaster. The compound was prepared via a chiral pool approach. An allylic C15 bromide, prepared from eicosapentaenoic acid (EPA) following a published procedure, was used as the ωend fragment. It was attempted to transform the resulting bromide into the corresponding magnesium bromide for the planned reaction with D-125. With the Wurtz coupling of the C15 bromide being the major product, it was concluded that the addition to D-125 failed. In previous work in our group a α-sulfonyl carbanion has been added to an aldehyde. The sulfone was prepared and reacted with D-125. The addition resulted in a mixture of four isomers of the 4- sulfonyl-3-hydroxyl-2-amine. These were separated, desulfonated and deprotected to give crucigasterin 277, and thereby confirming the suggested structure. Paper IV describes the synthesis of obscuraminol A, a sphingolipid. Instead of using the chiral pool approach, we planned a strategy utilizing an asymmetric nitroaldol reaction (Henry reaction). The corresponding C15 alcohol was made according to published procedures starting with commercially available EPA. Homologation gave a C16 aldehyde. This aldehyde was subjected to nitroethane, in the presence of base, and a chiral proline-derived catalyst. This resulted in a nitro alcohol, which was reduced using SmI2 to give the sphingolipid obscuraminol A.Artikkel I beskriver totalsyntesen av mucosin, en C20 fettsyre, isolert fra middelhavssvampen, Reniera mucosa. Syntesen startet med en tre-trinns syntese av et kjent meso-keton. Dette meso-ketonet ble omdannet til en optisk aktiv βketoester, også kjent fra litteraturen. I en tretten trinns sekvens, som blant annet inkluderer en kobber-katalysert krysskobling og kombinert aluminering/halodemetallering/Negishi krysskobling, ble den foreslåtte strukturen av (-)-mucosin syntetisert. Sammenligning av spektrale data fra litteraturen avdekket uoverensstemmelser. Røntgenkrystallografi av et mellomprodukt viste at den foreslåtte strukturen mest sannsynlig ikke kan være korrekt. Artikkel II beskriver den totale syntese av diastereomeren av den foreslåtte strukturen til mucosin. Vi dro nytte av den samme ketoesteren fra artikkel I, for å lage en α, β-umettede ester. Denne ble benyttet i konjugert addisjon for å skape et invertert motiv. Ved denne strategien klargjorde vi anti-diastereomeren av den foreslåtte strukturen for mucosin. Dette viser at naturproduktet mest sannsynlig ikke inneholder en cis-fusjonert, bisyklisk kjerne. Dette fordi det fremstilte materialet ikke samsvarte med de rapporterte data. Artikkel III beskriver syntesen av crucigasterin 277, et sfingolipid isolert fra et kappedyr fra middelhavsområdet, Pseudomonas crucigaster. Forbindelsen ble fremstilt via en “chiral pool” tilnærming, der aminoalkohol-delen ble hentet fra D-alaninal. Et umettet, allylisk C15-bromid, fremstilt fra eikosapentaensyre (EPA) ved å følge litteraturprosedyrer ble anvendt som ω-fragment. Denne ble forsøkt omdannet til det tilsvarende allyliske Grignard-reagenset, etterfulgt av reaksjon med D-alaninal. Dette ga Wurtz-produkt av C15-bromid som hovedprodukt. Gruppen vår har tidligere erfaringer med å benytte sulfoner i slike koblinger, og C15-sulfonet ble laget fra C15-bromidet. Dette sulfonet ble reagert med alaninal, og resulterte i en blanding av fire isomerer av sulfoyl hydroksylamin. Disse ble separert, desulfonert og avbeskyttet for å gi sfingolipidet crucigasterin 277. Dermed ble strukturen av crucigasterin 277 bekreftet. Artikkel IV beskriver syntesen av obscuraminol A, en sfingolipid med likheter til crucigasterin 277. I stedet for å bruke «chiral pool» tilnærmingen benyttet i Paper II, ble en asymmetrisk nitroaldol reaksjon benyttet. Mye av de samme reaksjonene som ble benyttet i foregående publikasjoner (”Paper II”), ble anvendt for å fremstille en C15 alkohol. Denne alkoholen ble homologert til et C16 aldehyd. Dette aldehydet ble reagert med nitroetan i nærvær av base og en kiral katalysator basert på prolin. Dette resulterte i en nitroalkohol, som ble redusert ved bruk av SmI2 for å gi sfingolipidet obscuraminol A

Syntese mot chamigren (et sesquiterpen)

Det ble lagt en strategi for å finne en forenklet syntese av det bisykliske sesquiterpenet, β-chamigren (1). Chamigrener er funnet i en rekke planter, men er først og fremst vanlig i alger, spesielt av slekten Laurencia[1]. Strategien for å syntetisere β-chamigren kan grovt sett deles i to, der den første delen er syntese av det umettede ketonet 3,3-dimetyl-2-metylen-sykloheksanon (25). Denne delen av syntesen er basert på metoder fra en tidligere publisert syntese av β-chamigren[1][2]. Startmaterialet var et billig, kommersielt tilgjengelige keton, 6-metylhept-5-en-2-one. Dette ble reagert med dimetylkarbonat og produktet syklisert til en seksring. Både ketonet og esteren ble redusert med litiumaluminiumhydrid, og det ble satt en beskyttelsesgruppe, tosylat, på primære alkoholen. Sekundæralkoholen ble så oksidert tilbake til keton, tosylat-gruppen fjernet med DBU til det umettede ketonet, 3,3-dimetyl-2-metylen-sykloheksanon. I den andre delen av strategien ble det umettede ketonet benyttet videre i en hetero-Diels-Alder ved hjelp av mikrobølgeoppvarming. Diels-Alder-produktet skulle så blitt omdannet til et bisyklisk aldehyd som videre kan olefineres. Via Claisen-Cope-omleiring og nok en olefinering skulle dette gitt β-chamigren. Diels-Alder ble prøvd ut med både metakrylaldehyd, metakrylnitril og etylmetakrylat som dienofil. De to førstnevnte ga dårlige resultater, mens reaksjonen med etylmetakrylat ga et utbytte på 78 % ved 160˚C i 10 minutter (rask oppvarming på 30 sekunders benyttet). Samme reaksjon er gjort tidligere med metylmetakrylat og tradisjonell oppvarming, men da ble utbytte kun på 44 % etter 12timer ved 190˚C[1]. For å gi det bisykliske aldehydet ble etylesteren forsøkt redusert. Det ble prøvd reduksjon med DIBAL uten hell. Det ble da forsøkt å redusere esteren helt til primær alkohol med litiumaliminiumhydrid, men også dette uten hell. Det ble ikke funnet noen måte å syntetisere aldehydet på, så syntesen var ikke vellykket. På slutten av oppgaven er det nevnt noe videre arbeid som kan utprøves. The goal was to make a strategy to simplify the synthesis β-chamigren (1), a bicyclic sesqiterpen. β-chamigrene has been found in several plants, but most commonly found in algae, especially of the genus Laurencia. The strategy was divided into two parts: synthesis of unsaturated ketone, 3,3-dimethyl-2-methylene-syklohexanone (25). This first part was based on methods from a previously published β-chamigrene synthesis[1][2]. The starting material was an inexpensive, commercially available ketone, 6-methylhept-5-en-2-one. Reacting this with dimetylcarbonate gave the six membered cyclo ketoester in two steps. Both the ketone and the ester were reduced to alcohols with litiumaluminiumhydride. The primary alcohol was tosylated and the secondary oxidized to the ketone. Using DBU to remove α-protons gave 3,3-dimethyl-2-methylene-syklohexanone. The secondary part of the strategy was using this unsaturated ketone in a hetero-Diels-Alder using a microwave oven. Converting the Diels-Alder product into a bicyclic aldehyde, that can form an olefin via Wittig or Peterson olefination. Reacting this via a Claisen rearrangement followed by an olefination should result in β-chamigrene. Both methacrylaldehyde, methacrylonitrile and ethyl methacrylate were used as dienophiles in the Diels-Alder-reaction in order to determine which ones will give the best results. After all: in theory both the ester and the nitrile could be reduced to the aldehyde with DIBAL. The reactions with the aldehyde and the nitrile were not successful. The reaction with the ester on the other hand gave 78 % yield under the reactions conditions of 160˚C for 10 minutes (in addition 30 seconds were used to reach this temperature). A similar reaction without microwave oven gave 44 % yield using methyl methacrylate with the reaction conditions of 12 hours and 190˚C [1]. It was attempted to get the bicyclic aldehyde reducing the ester with DIBAL. This reduction was unsuccessful. Lithium aluminium hydride was used to reduce it all the way to the alcohol, which in theory could be oxidized to the aldehyde. This approach was also unsuccessful. We did not discover an approach that resulted in the aldehyde. Later in this thesis some alternative approaches will be suggested

Stereopermutation on the Putative Structure of the Marine Natural Product Mucosin

A stereodivergent total synthesis has been executed based on the plausibly misassigned structure of the unusual marine hydrindane mucosin (1). The topological connectivity of the four contiguous all-carbon stereocenters has been examined by selective permutation on the highlighted core. Thus, capitalizing on an unprecedented stereofacial preference of the cis-fused bicycle[4.3.0]non-3-ene system when a Michael acceptor motif is incorporated, copper-mediated conjugate addition furnished a single diastereomer. Cued by the relative relationship reported for the appendices in the natural product, the resulting anti-adduct was elaborated into a probative target structure 1*

Synthesis towards β-chamigrene (a sesquiterpene)

Det ble lagt en strategi for å finne en forenklet syntese av det bisykliske sesquiterpenet, β-chamigren (1). Chamigrener er funnet i en rekke planter, men er først og fremst vanlig i alger, spesielt av slekten Laurencia[1]. Strategien for å syntetisere β-chamigren kan grovt sett deles i to, der den første delen er syntese av det umettede ketonet 3,3-dimetyl-2-metylen-sykloheksanon (25). Denne delen av syntesen er basert på metoder fra en tidligere publisert syntese av β-chamigren[1][2]. Startmaterialet var et billig, kommersielt tilgjengelige keton, 6-metylhept-5-en-2-one. Dette ble reagert med dimetylkarbonat og produktet syklisert til en seksring. Både ketonet og esteren ble redusert med litiumaluminiumhydrid, og det ble satt en beskyttelsesgruppe, tosylat, på primære alkoholen. Sekundæralkoholen ble så oksidert tilbake til keton, tosylat-gruppen fjernet med DBU til det umettede ketonet, 3,3-dimetyl-2-metylen-sykloheksanon. I den andre delen av strategien ble det umettede ketonet benyttet videre i en hetero-Diels-Alder ved hjelp av mikrobølgeoppvarming. Diels-Alder-produktet skulle så blitt omdannet til et bisyklisk aldehyd som videre kan olefineres. Via Claisen-Cope-omleiring og nok en olefinering skulle dette gitt β-chamigren. Diels-Alder ble prøvd ut med både metakrylaldehyd, metakrylnitril og etylmetakrylat som dienofil. De to førstnevnte ga dårlige resultater, mens reaksjonen med etylmetakrylat ga et utbytte på 78 % ved 160˚C i 10 minutter (rask oppvarming på 30 sekunders benyttet). Samme reaksjon er gjort tidligere med metylmetakrylat og tradisjonell oppvarming, men da ble utbytte kun på 44 % etter 12timer ved 190˚C[1]. For å gi det bisykliske aldehydet ble etylesteren forsøkt redusert. Det ble prøvd reduksjon med DIBAL uten hell. Det ble da forsøkt å redusere esteren helt til primær alkohol med litiumaliminiumhydrid, men også dette uten hell. Det ble ikke funnet noen måte å syntetisere aldehydet på, så syntesen var ikke vellykket. På slutten av oppgaven er det nevnt noe videre arbeid som kan utprøves. The goal was to make a strategy to simplify the synthesis β-chamigren (1), a bicyclic sesqiterpen. β-chamigrene has been found in several plants, but most commonly found in algae, especially of the genus Laurencia. The strategy was divided into two parts: synthesis of unsaturated ketone, 3,3-dimethyl-2-methylene-syklohexanone (25). This first part was based on methods from a previously published β-chamigrene synthesis[1][2]. The starting material was an inexpensive, commercially available ketone, 6-methylhept-5-en-2-one. Reacting this with dimetylcarbonate gave the six membered cyclo ketoester in two steps. Both the ketone and the ester were reduced to alcohols with litiumaluminiumhydride. The primary alcohol was tosylated and the secondary oxidized to the ketone. Using DBU to remove α-protons gave 3,3-dimethyl-2-methylene-syklohexanone. The secondary part of the strategy was using this unsaturated ketone in a hetero-Diels-Alder using a microwave oven. Converting the Diels-Alder product into a bicyclic aldehyde, that can form an olefin via Wittig or Peterson olefination. Reacting this via a Claisen rearrangement followed by an olefination should result in β-chamigrene. Both methacrylaldehyde, methacrylonitrile and ethyl methacrylate were used as dienophiles in the Diels-Alder-reaction in order to determine which ones will give the best results. After all: in theory both the ester and the nitrile could be reduced to the aldehyde with DIBAL. The reactions with the aldehyde and the nitrile were not successful. The reaction with the ester on the other hand gave 78 % yield under the reactions conditions of 160˚C for 10 minutes (in addition 30 seconds were used to reach this temperature). A similar reaction without microwave oven gave 44 % yield using methyl methacrylate with the reaction conditions of 12 hours and 190˚C [1]. It was attempted to get the bicyclic aldehyde reducing the ester with DIBAL. This reduction was unsuccessful. Lithium aluminium hydride was used to reduce it all the way to the alcohol, which in theory could be oxidized to the aldehyde. This approach was also unsuccessful. We did not discover an approach that resulted in the aldehyde. Later in this thesis some alternative approaches will be suggested.The goal was to make a strategy to simplify the synthesis β-chamigren (1), a bicyclic sesqiterpen. β- chamigrene has been found in several plants, but most commonly found in algae, especially of the genus Laurencia. The strategy was divided into two parts: synthesis of unsaturated ketone, 3,3-dimethyl-2-methylene-syklohexanone (25). This first part was based on methods from a previously published β-chamigrene synthesis[1][2]. The starting material was an inexpensive, commercially available ketone, 6-methylhept-5-en-2-one. Reacting this with dimetylcarbonate gave the six membered cyclo ketoester in two steps. Both the ketone and the ester were reduced to alcohols with litiumaluminiumhydride. The primary alcohol was tosylated and the secondary oxidized to the ketone. Using DBU to remove α-protons gave 3,3-dimethyl-2-methylene-syklohexanone. The secondary part of the strategy was using this unsaturated ketone in a hetero-Diels-Alder using a microwave oven. Converting the Diels-Alder product into a bicyclic aldehyde, that can form an olefin via Wittig or Peterson olefination. Reacting this via a Claisen rearrangement followed by an olefination should result in β-chamigrene. Both methacrylaldehyde, methacrylonitrile and ethyl methacrylate were used as dienophiles in the Diels-Alder-reaction in order to determine which ones will give the best results. After all: in theory both the ester and the nitrile could be reduced to the aldehyde with DIBAL. The reactions with the aldehyde and the nitrile were not successful. The reaction with the ester on the other hand gave 78 % yield under the reactions conditions of 160˚C for 10 minutes (in addition 30 seconds were used to reach this temperature). A similar reaction without microwave oven gave 44 % yield using methyl methacrylate with the reaction conditions of 12 hours and 190˚C [1]. It was attempted to get the bicyclic aldehyde reducing the ester with DIBAL. This reduction was unsuccessful. Lithium aluminium hydride was used to reduce it all the way to the alcohol, which in theory could be oxidized to the aldehyde. This approach was also unsuccessful. We did not discover an approach that resulted in the aldehyde. Later in this thesis some alternative approaches will be suggested.2017-05-15M-KJEM

Total synthesis as a tool for structural elucidation of some marine lipid natural products

Paper I describes the total synthesis of the proposed structure of mucosin, a C20 fatty acid, isolated from a Mediterranean sponge, Reniera mucosa. The synthetic pathway started with the transformation of 1,4-cyclohexadiene to a known meso-ketone in three steps. Employing a chiral base, an optically active β-keto ester, also previously described in literature, was obtained in excellent stereochemical purity. In a thirteen-step linear sequence, including a copper mediated cross-coupling, onepot alumination/halodemetallation/Negishi cross-coupling protocol, gave the proposed structure of (-)-mucosin. Comparison of spectral data with the literature reported values revealed discrepancies. By employing X-ray crystallography on a late stage intermediate, it was demonstrated that the relative stereochemistry assigned to mucosin had been achieved. This also proved that the structure claimed in literature is most likely incorrect. Paper II describes the total synthesis of the diastereomer of the proposed structure of mucosin. Taking advantage of the same keto ester from paper I, we prepared an α,β-unsaturated ester enabling an inverted motive for the conjugate addition. By this strategy we made the anti-diastereomer of the proposed structure for mucosin. This demonstrated that the natural product most likely does not contain a cis-fused bicyclic core, since the prepared material did not match the reported data. Paper III describes the synthesis of crucigasterin 277, a sphingolipid isolated from the Mediterranean tunicate, Pseudomonas crucigaster. The compound was prepared via a chiral pool approach. An allylic C15 bromide, prepared from eicosapentaenoic acid (EPA) following a published procedure, was used as the ωend fragment. It was attempted to transform the resulting bromide into the corresponding magnesium bromide for the planned reaction with D-125. With the Wurtz coupling of the C15 bromide being the major product, it was concluded that the addition to D-125 failed. In previous work in our group a α-sulfonyl carbanion has been added to an aldehyde. The sulfone was prepared and reacted with D-125. The addition resulted in a mixture of four isomers of the 4- sulfonyl-3-hydroxyl-2-amine. These were separated, desulfonated and deprotected to give crucigasterin 277, and thereby confirming the suggested structure. Paper IV describes the synthesis of obscuraminol A, a sphingolipid. Instead of using the chiral pool approach, we planned a strategy utilizing an asymmetric nitroaldol reaction (Henry reaction). The corresponding C15 alcohol was made according to published procedures starting with commercially available EPA. Homologation gave a C16 aldehyde. This aldehyde was subjected to nitroethane, in the presence of base, and a chiral proline-derived catalyst. This resulted in a nitro alcohol, which was reduced using SmI2 to give the sphingolipid obscuraminol A

Synthesis of Racemic β-Chamigrene, a Spiro[5.5]undecane Sequiterpene

The present paper describes a total synthesis of racemic β-chamigrene (1), a sesquiterpene with a spiro[5.5]undecane carbon framework. Compared with previously reported β-chamigrene syntheses, we were able to reduce the total number of reaction steps, which also resulted in a significant improvement of the overall yield. The commercially available ketone 6-methylhept-5-en-2-one was transformed by known simple procedures into 3,3-dimethyl-2-methylenecyclohexanone. This reacted with isoprene by a Diels-Alder reaction to give a spiro ketone. An olefination reaction on this compound gave the target molecule