ORGN 41 |
| Incorporation of a fluorine substituent in thiirane 1 greatly increased the SN2 reaction rate with NH3. We now report this rate-enhancing effect persists when MP2(Full)/6-311++G(d,p)//MP2(Full)/6-31+G(d) calculations are performed, and include 2-fluorooxirane 2 and 2-fluoroaziridine 3. Unlike thiirane and oxirane, aziridines are typically converted to their N-acetyl or N-sulfonyl derivatives to improve reactivity. The discovery for 3 potentially may extend the synthetic utility of aziridines. Attack on 3 and 6 was calculated to occur highly regioselectively at the 3-position. Ammonia cleaved the heterocyclic ring of trans-isomer 4 about 1.0E+08 times faster than its diastereomer 5; it is noteworthy that reaction rate for both these compounds was greater than that found for 3 at the 2-position even though geminal attack must occur for 4 and 5. The most reactive compound was 6. Release of strain energy and charge effects are included in rationalizing of the relative rates for the fluorinated aziridines.
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
8:00 AM-11:40 AM, Sunday, 10 September 2006 Moscone Center -- Room 133, Oral
Division of Organic Chemistry |
