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Asymmetric Electrophilic α‐Amidoalkylation, VII 1) : Generation, Crystal Structure, and Trapping Reactions of a Chiral 6,7‐Dimethoxy‐1,2,3,4‐tetrahydroisoquinoline Derived N‐Acyliminium Ion
Author(s) -
Wanner Klaus Th.,
Praschak Ilona,
Nagel Ulrich
Publication year - 1990
Publication title -
archiv der pharmazie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.468
H-Index - 61
eISSN - 1521-4184
pISSN - 0365-6233
DOI - 10.1002/ardp.19903230605
Subject(s) - chemistry , iminium , tetrafluoroborate , crystal structure , diastereomer , electrophile , nucleophile , yield (engineering) , amide , stereoselectivity , medicinal chemistry , ion , silylation , stereochemistry , crystallography , organic chemistry , catalysis , ionic liquid , metallurgy , materials science
The camphanic acid amide 4 has efficiently been oxidized with triphenylcarbenium tetrafluoroborate ( 3 ) to yield the chiral N‐acyliminium ion 1 . Trapping reactions of 1 with the silyl nucleophiles 7a‐c and 10a‐f proceeded with stereoselective bond formation, affording the diastereomers (R)‐ 8 /(S)‐ 9a‐c and (R)‐ 11 /(S)‐ 12a‐f , respectively, with diastereoselectivities of up to 93.9/6.1. The amido ketones (R)‐ 8 /(S)‐ 9a‐c were employed in the synthesis of the secondary amines (R)‐ 16a‐c , (S)‐ 16a and for the preparation of (−)‐homolaudanosine (R)‐ 18 . By X‐ray crystallography the conformation of 1 in the crystal lattice was established and the preferred conformation of 1 in solution was elucidated by NOE experiments. Finally, the addition reaction of 7a to the iminium ion 21 derived from menthyl carbamate 20 was investigated, which reaction, however, proceeded only with insignificant asymmetric induction.