1,5-(H, RO, RS) shift/6π-electrocyclic ring closure tandem processes on N-[(α-heterosubstituted)-2-tolyl]ketenimines: a case study of relative migratory aptitudes and activating effectsElectronic supplementary information (ESI) available: ORTEP representation of the crystal structure of cis-20e. Copy of 1H and 13C NMR spectra of compounds 10, 12, 13, 17, 20, 21, 26, 28, 31, 34, 37 and 39. Copy of 31P NMR spectra of compounds 10, 17, 26, 31 and 37. Cif files of cis-20e. CCDC 905526. For ESI and c

A number of N -aryl ketenimines, substituted at the ortho position either with different non-cyclic acetalic functions (acetals, monothioacetals, dithioacetals) or with only one alkoxymethyl or (alkylthio)methyl group, have been prepared and submitted to thermal treatment in toluene solution. Under smooth heating the ketenimines bearing non-cyclic acetals converted into 3,4-dihydroquinolines following two competitive tandem sequences that involve the alternative 1,5 migration of a hydride or alkoxy group as the first mechanistic step, followed by subsequent 6π electrocyclic ring closure. The heterocumulenes bearing acyclic monothioacetal and dithioacetal functions converted via a unique consecutive process involving the selective migration of the alkanethiolate group. Ketenimines bearing only one ether or thioether group transformed exclusively by the tandem sequence initiated by a 1,5 hydride shift. All these transformations provided as final reaction products a variety of quinoline derivatives with a range of substitution patterns. From these experiments the following order of propensity to migration can be extracted: RS > RO > H. It was also possible to estimate the following order of relative activating activities: RO > RS > H. N -(2-Substituted)aryl ketenimines (structures shown) converted into 3,4- dihydroquinolines via a consecutive process involving the migration of hydride, alkoxy or alkanethiolate groups followed by a 6π electrocyclization.