Intramolecular [4 + 2] cycloaddition reaction of six- and seven-membered cyclic N-allyl-C-arylethynyl iminium salts |
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Authors: | Herz H G Schatz J Maas G |
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Institution: | Abteilung Organische Chemie I, Universit?t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany. |
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Abstract: | N-Allyl-2-(het)arylethynyl-3,4,5,6-tetrahydropyridinium triflates 1c,d,e and N-allyl-2-(het)aryl-4,5,6,7-tetrahydro-3H-azepinium triflates 1g,h undergo a thermal isomerization reaction leading to derivatives of a,f]-annulated isoindolium salts 2 in good yields. Similarly, N-allyl-2-phenylethynyl-pyridinium triflate 4 is transformed into the condensed pyridinium salt 5. An intramolecular 4 + 2] cycloaddition reaction, in which the (het)arylethynyl moiety acts as the 4pi component, is considered as the key step of this transformation. In contrast, the related N-allyl-4,5-dihydro-3H-pyrrolium salts 1a,b and N-homoallyl-3,4,5,6-tetrahydropyridinium salt 1f undergo unspecific decomposition under thermal impact. |
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