title: Intramolecular [4 + 2] cycloaddition reaction of six- and seven-membered cyclic N-allyl-C-arylethynyl iminium salts.
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.
authors.affiliation: Abteilung Organische Chemie I, Universität Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: H G
authors.initials: HG
authors.lastname: Herz
authors.forename: J
authors.initials: J
authors.lastname: Schatz
authors.forename: G
authors.initials: G
authors.lastname: Maas