Controlling neighbouring group participation from thioacetals |
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Authors: | Mairi GibsonJonathan M Goodman Louis J FarrugiaRichard C Hartley |
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Institution: | a Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK b Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK |
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Abstract: | A 1,3-dithiane displaces tosylate by a 5-exo-tet cyclisation to give a bicyclic sulfonium salt. Nucleophilic attack on this 4-thia-7a-thioniaperhydroindene by azide ions kinetically favours opening to give a nine-membered ring α-azidosulfide, but 2-(3′-azidopropyl)-1,3-dithiane is the thermodynamic product from B3LYP/6-31G** calculations. A similar sulfonium salt generated from 2-(3′-hydroxypropyl)-1,3-dithiane with thionyl chloride rearranges to 2-(3′-chloropropyl)-1,3-dithiane. Azide ion displacement of the primary alkyl chloride is then faster than 1.4] sulfanyl participation from the thioacetal. An α-chlorosulfide derived from diphenyldithioacetal does not rearrange but undergoes direct displacement to give an α-azidosulfide. |
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Keywords: | thioacetal sulfonium salt neighbouring group participation α-chlorosulfide azide kinetic control thermodynamic control calculation medium ring |
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