NEW STRATEGIES FOR ENANTIOSELECTIVE SYNTHESES OF 1-ALKYL-1,2,3,4-TETRAHYDROISOQUINOLINES AND 1,4-DIALKYL-1,2,3,4-TETRAHYDROISOQUINOLINES - DIASTEREOSELECTIVE ADDITIONS OF NUCLEOPHILES AND ELECTROPHILES TO ISOQUINOLINE MEDIATED BY AN EASILY RESOLVED AND RECYCLED CHIRAL TRANSITION-METAL AUXILIARY

The chiral rhenium isoquinoline complex [(eta5-C5H5)Re(NO)(PPh3)(iso-NC9H7)]+ TfO- (1) and (CH3)3-SiCH2Li give the addition product (eta5-C5H5)Re(NO)(PPh3)(NCH=CHC(CH)4CCHCH2Si(CH3)3) (2) in 71% yield as a 94:6 SS,RR/SR,RS diastereomer mixture. Similar reactions with RMgX (R = (CH3)2CH, CH3CH2, C6H5CH2, CH3(CH2)2, CH3, CH3(CH2)3) give analogous adducts (3-8) as 89-82:11-18 diastereomer mixtures. Reactions of 2 and ROTf (R = H/D, (CH3)3SiCH2, CH3) give alkyl-1,4-dihydroisoquinoline complexes [(eta5-C5H5)Re(NO)-(PPh3)(N=CHCHRC(CH)4CCHCH2Si(CH3)3)]+ TfO- in 84-72% yields as 94:6 diastereomer mixtures. Related complexes are prepared from 3-5 and HOTf. These react with NaBH4/CH3OH to give alkyl-1,2,3,4-tetrahydroisoquinoline complexes, which are in turn treated with (CH3CH2)4N+ CN- to give (eta5-C5H5)Re(NO)(PPh3)(CN) (17) and the title compounds. A reaction sequence starting with (+)-(S)-1 and (CH3)3SiCH2Li yields (+)-(SS)-NHCH2-CH(CH2Si(CH3)3)C(CH)4CCHCH2Si(CH3)3 (84% overall, 88% ee) and (+)-(S)-17(82%, >98% ee). Other optically active alkyl tetrahydroisoquinolines are similarly prepared. Complexes 17 and (+)-(S)-17 are converted to (eta5-C5H5)Re(NO)(PPh3)(CH3) (CH3OTf/NaBH4; 88-53%) and thence to 1 or (+)-(S)-1 (92-74%, >98% ee). A crystal structure and other data confirm the configurations assigned to the preceding compounds.