A general procedure for the synthesis of 1-benzyl-1,2,3,4-tetrahydroisoquinolines was developed, based on organocatalytic,
regio- and enantioselective Pictet-Spengler reactions (86-92% ee) of N-(o-nitrophenylsulfenyl)-2-arylethyl-amines with arylacetaldehydes.
The presence of the o-nitrophenylsulfenyl group, together with the MOM-protection in the catechol part of the tetrahydroisoquinoline
ring system, appeared to be a productive combination. To demonstrate the versatility of this approach, 10 biologically and
pharmaceutically relevant alkaloids were prepared using (R)-TRIP as the chiral catalyst: (R)-norcoclaurine, (R)-coclaurine,
(R)-norreticuline, (R)-reticuline, (R)-trimemetoquinol, (R)-armepavine, (R)-norprotosinomenine, (R)-protosinomenine, (R)-laudanosine,