Bulletin of the Chemical Society of Japan · 1982 · 20 citations · 9 references
Natural SciencesChemistryMedicinal ChemistryOrganic ChemistryOrganometallic ChemistrySynthetic Medicinal ChemistryHeterocycle SynthesisHeterocyclic ChemistryHeterocyclic CompoundsOrganic SynthesisRadical ReactionsRetrosynthetic AnalysisBenzothiazole SynthesisMigratory AptitudeNucleophilic ReactivityRearrangement ReactionsThiazole ChemistryThiazole Synthesis
Abstract Alkylation of 2-substituted 3-methyl- or 3-ethylbenzothiazolines with Meerwein reagents gave 2-substituted 3,3-dialkylbenzothiazolinium tetrafluoroborates (3). The configuration of two alkyl groups on the nitrogen was assigned by NMR spectra and NOE measurement. In the Stevens rearrangement of 3 with lithium diisopropylamide ethyl group showed a much larger migratory aptitude (Et:Me≥20 :1) than methyl group irrespective of the configuration of 3, and cyclic ammonium ylide with planar π-type carbanion was proposed as an intermediate. 3 suffered nucleophilic attack at the ring sulfur atom by butyllithium to afford a ring-opened ammonium ylide, which collapses to a radical pair to give unusual Stevens rearrangement product, where o-alkylthiophenyl group migrated selectively in preference to alkyl group, because of stabilization by participation of o-alkylthio group.
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