Organocatalytic Asymmetric Synthesis of trans-1,3-Disubstituted Tetrahydroisoquinolines via a Reductive Amination/Aza-Michael Sequence
作者:Dieter Enders、Jens X. Liebich、Gerhard Raabe
DOI:10.1002/chem.201001623
日期:2010.8.23
Benzothiazoline better than Hantzsch: A stereoselective Brønsted acid catalyzed reductive amination/aza‐Michael approach towards the important class of tetrahydroisoquinolines is presented (see scheme). A biphenyl‐substituted benzothiazoline is used as the reducing agent and leads to superior yields and enantiomeric excesses compared with the frequently used Hantzsch ester. The cyclization of the amine
lithiation followed by acylation with aroyl chlorides. 8,9-Dialkoxy-2,3-benzodiazepines 9 were obtained by cyclisation of diketones 6 with hydrazine. The reaction of diketones 6 with ammonia gave 7,8-dialkoxyisoquinolines 11. Reaction of ketals 5 with hydrazine hydrochloride and hydroxylamine hydrochloride afforded N-amino-7,8-dialkoxyisoquinolinium chlorides (10) and 7,8-dialkoxyisoquinolinium oxides (12)