Some observations on the enantio- and diastereo-selective synthesis of 1-substituted-1,2,3,4-tetrahydro iosquinolines

Abstract

Several approaches to the synthesis of optically active 1-aryl- 1,2,3,4-tetrahydroisoquinoline alkaloids, crptostylines (1-3) from dihydrorsoquinoline precursors 5,6,11 and 12 have been tried. Reductions of the I-aryldihydralsoquinoline 5 and the 1-methyl analogue 7 as well as of their methiodides 6 and 9 with yeast are unsuccessful. Reduction of the quaternary salts 6,11,12 and 9 with sodium tris-acylaxyborohydrides gives the tetrahydroisoquinollne alkaloids 1-3 and 10, respectively, in unsatisfactory enantiomeric excess.(+-) Norcryptostyline 4 is resolved with (-)and (+) tartaric acid into (-)S and (+)R enantiomers 14 and 17, respectively, which are converted to  their camphorsulphonyl derivatives 15 and 16. Reaction of camphorsulphonyl hamoveratryi amine 13 with personal affords a mixture of 16 and 15 In the ratio of 4:3, whereas campharsulphonylation of racemlc 4 gives 16 much in excess of 15 (4:l).