An enantioselective synthesis of isoquinuclidines from 3-substituted chiral pyridinium salts

A new enantioselective approach to chiral isoquinuclidines, such as 15, 18 and 21, is reported. The key step of these syntheses is a cycloaddition between chiral dihydropyridines 14 or 20, now readily available from tetrahydropyridinium salts 6 or 11, and achiral dienophiles. The reaction proceeds with a very good endo-selectivity and moderate d.e.