The directed dihydroxylation of allylic amides
Başlık:
The directed dihydroxylation of allylic amides
Yazar:
Winter, Jonathan J. G., author.
ISBN:
9780438043800
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (251 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
A study of stereo- and regioselectivity in the syn-syn dihydroxylation of allylic amides, using both stoichiometric and catalytic quantities of osmium tetroxide, is described. Existing osmium tetroxide dihydroxylation methodology favours the formation of the syn diol product where the diol moiety is anti relative to other groups in the molecule. This work utilises the allylic amide as a directing group to encourage syn dihydroxylation in a conformation which is also syn to the amide. Introduction The various dihydroxylation reactions using osmium tetroxide will be detailed, to provide a background from which to contrast the newly developed methodology which this thesis concerns. Results and Discussion Optimisation of conditions. This section details the results obtained while the directed dihydroxylation reaction was being optimised; the various protecting groups which were used and the large array of ligands which were screened once a suitable group had been found. Cyclic stereocontrol. This section describes the work which was undertaken to prove the directed osmylation was a stereoselective process, and was general with a large number of substrates. Synthesis of the starting materials, the dihydroxylation methodologies used, the selectivities observed in reactions and the methods used to prove the relative stereochemistry of products are all described. Catalytic syn-syn selective dihydroxylation. This section details the progress made towards a catalytic variant of the syn-syn osmylation, the selectivities obtained, and a hypothesis explaining the selectivity observed. Cyclic and acyclic regiocontrol This section explores the results obtained from experiments designed to show the osmylation was also a regioselective process. Synthesis of starting materials, general methodology, selectivity results and proof of regiochemical selectivity (as well as stereochemical when appropriate) is be covered. Oxidative cyclisation to form cis-tetrahydrofurans. This section discusses the unexpected reaction which is observed when 1,5-dienyl trichloroacetamides are subjected to the osmylation conditions described earlier. Synthesis of these materials, proof of stereochemistry of the products, an overview of similar cyclisation reactions in the literature and a postulated mechanism are included in this section. Partial synthesis of angolosamine. Synthesis of the rare natural sugar angolosamine was attempted, using the novel dihydroxylation reaction described above. Good levels of acyclic stereocontrol were achieved, and the sequence continued as far as time would allow. This section also covers the proposed steps to complete the synthesis, and discusses a possible route for a chiral non-racemic synthesis of the same material.
Notlar:
School code: 1543
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684317.1) | 684317-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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