Transformation of (+)-thiomicamine into chiral non-racemic 3,4-dihydroisoquinolinium salts: application for catalytic asymmetric epoxidation of alkenes and oxidation of sulfides

(1S,2S)-(+)-Thiomicamine 7 (R=SCH3) has been transformed into (3S,4R)-2,3-dimethyl-4-phenyl-3,4-dihydroisoquinolinium tetrafluoroborate 2 in a five-step reaction sequence involving (3S,4R)-2,3-dimethyl-1,2,3,4-tetrahydroisoquinolinie 14 as the key intermediate. Iminium salt 16 has been evaluated as a promoter of catalytic asymmetric epoxidation of trans-stilbene and oxidation of methyl-p-tolyl sulfide, affording products in satisfactory yield and with enantioselectivities up to 45% and 42%, ee, respectively. (C) 2004 Elsevier Ltd. All rights reserved.