Ascic, Erhad

Kapitel 1. En ’’build/couple/pair’ strategi der kombinerer Petasis 3-komponent  reaktionen og Ru-katalyseret ringlukningsmetatese  En ‘‘build/couple/pair’’ strategi til effektiv og koncis (2-5 trin) syntese af strukturelt forskellige forbindelser er beskrevet. En Petasis reaktion anvendes til syntese af antiaminoalkoholer, der indeholder parvist reaktive kombinationer af alkengrupper. Under indflydelse af en ruthenium alkyliden-katalysator undergår disse diener  ringlukningsmetatese og danner en række forskellige heterocykler. Ydermere er der blevet udviklet en ruthenium-katalyseret tandem RCM/isomerisering/N-alkyliminium cykliseringssekvens til dannelse af hidtil ukendte oxazabicyclooctane-derivater, der representerer et ekstra element af skeletal diversitet. En række diversifikationsreaktioner er blevet undersøgt, bla. palladium-katalyserede ring-kontraktioner og  intramolekylære Diels-Alder reaktioner. Kapitel 2. Multifunktionell katalyse: Syntese af heterocykler fra simple udgangsmaterialer. En multifunktionel katalysestrategi, der involverer ruthenium-katalyseret tandem ringlukningsmetatese/isomerisering/N-acylliminium cykliseringssekvens, er beskrevet. Dobbeltbindinger dannet under ringlukningsmetatese isomeriseres til reaktive Nacyliminium ioner, der undergår intramolekylære cykliseringsreaktioner i tilstedeværelse af heteroatom- og carbonnukleofiler. To nye ringe dannes i denne tandem process, hvor et enkelt metal katalyser to mekanistisk forskellige reaktioner i en kemisk operation. På denne måde dannes en række interessante indolizidinoner i gode udbytter med fremragende diastereoselektiviteter, herunder udføres der en formel totalsyntese af det antiparasistic naturprodukt harmicin og den første totalsyntese af mescalotam. Derudover er asymmetriske varianter af tandem-processen blevet undersøgt, og visse indolizinoindoler blev syntetiseret i op til 60% ee.Chapter 1. Build/Couple/Pair Strategy Combining the Petasis 3-Component Reaction with Ru-Catalyzed Ring-Closing Metathesis A “build/couple/pair” strategy for the efficient and concise (2-5 step) synthesis of structurally distinct skeletons is described. A Petasis 3-component reaction is used to synthesize anti-amino alcohols displaying pairwise reactive combinations of alkene moieties. Upon treatment with a ruthenium alkylidene catalyst, these dienes selectively undergo ring-closing metathesis reactions to form skeletally distinct heterocycles. In addition, a ruthenium-catalyzed tandem RCM/isomerization/Nalkyliminium cyclization sequence to hitherto unknown oxazabicyclooctane derivatives is developed which grants an extra element of skeletal diversity. Further skeletal diversification reactions utilizing palladium-catalyzed ring-contraction and intramolecular Diels-Alder reactions are also demonstrated. Chapter 2. Multifunctional Catalysis: Synthesis of Heterocycles from Simple Starting Materials A multifunctional catalysis approach, involving a ruthenium-catalyzed tandem ringclosing metathesis/isomerization/N-acyliminium cyclization sequence, is described. Double bonds created during ring-closing metathesis isomerize to generate reactive Nacyliminium intermediates which undergo intramolecular cyclization reactions with tethered heteroatom and carbon nucleophiles. In the tandem process, two new rings are formed, where a single metal catalyzes two mechanistically distinct reactions in one chemical operation. In this way, a series of interesting indolizidinones are formed in good yields with excellent diastereoselectivities, including a formal total synthesis of the antiparasitic natural product harmicine and the first total synthesis of mescalotam. Furthermore, preliminary asymmetric variants of the tandem process have been identified, affording indolizinoindoles in up to 60% ee.</p

Build/Couple/Pair and Multifunctional Catalysis Strategies for the Synthesis of Heterocycles from Simple Starting Materials

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