<p>Five-membered rings are readily prepared by <i>5-exo-trig</i> radical cyclization. This thesis is concerned with novel methodology for pyrrolidine synthesis. We have synthesised selenium containing radical precursors from aziridines and α-phenylseleno ketones, and cyclized them to 2,4- and 3,4-disubstituted pyrrolidines. A few examples of <i>5-exo-dig</i> cyclization were also demonstrated. In another study we investigated the capacity of the nitrogen protecting group to direct diastereoselectivity in the formation of 2,4-disubstituted pyrrolidines. The diphenylphosphinoyl protecting group directed cyclization to occur in a highly <i>cis</i>-selective manner. When cyclizations were performed at 17 <sup>o</sup>C, <i>cis</i>/<i>trans</i>-ratios as high as 24/1 were obtained. In contrast, cyclization of the unprotected pyrrolidine precursor afforded the <i>trans</i>-diastereomer as the major product (<i>cis</i>/<i>trans </i>= 1/3.3 – 1/20). We also examined the use of a hydroxyl auxiliary for controlling diastereoselectivity in radical cyclization. The required selenium containing radical precursors were synthesised from 2-cyanoaziridines by addition of organometallic reagents, reduction of the resulting aziridine ketone, and benzeneselenol ring-opening of the aziridine. Cyclization at 17 <sup>o</sup>C produced 2,4-disubstituted pyrrolidines substantially enriched in the <i>trans</i>-isomer (<i>cis</i>/<i>trans</i> = 1/9 – 1/12). Novel radical cyclization approaches to thiazolines and pyrrolines were also tried.</p><p>The thesis also describes attempts to improve the Hassner aziridine synthesis by employing stannous chloride as a functional group tolerant reducing agent.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-1954 |
| Date | January 2002 |
| Creators | Beşev, Magnus |
| Publisher | Uppsala University, Organic Chemistry, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 702 |
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