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Preparation of Chiral 2‐(2‐Bromobenzyl)‐1,3‐dioxolanes and Their Addition to Acylimines
Author(s) -
Wünsch Bernhard,
Nerdinger Sven
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199804)1998:4<711::aid-ejoc711>3.0.co;2-a
Subject(s) - chemistry , diastereomer , acetal , moiety , dioxolane , yield (engineering) , diol , enol , enantiomer , organic chemistry , stereochemistry , catalysis , materials science , metallurgy
A series of enantiomerically pure 2‐(2‐bromobenzyl)‐1,3‐dioxolanes 10 has been prepared by transacetalization of the dimethyl acetal 8 or the enol ether 7 with enantiomerically pure C 2 symmetric 1,2‐diols. We investigated the ability of the chiral 1,3‐dioxolane moiety to control the diastereoselectivity during the addition of the aryllithium intermediates 18 to the acylimines 17 . Those reactive aryllithium species were generated by bromine/lithium exchange at the bromo acetals 10 . In this series the best diastereoselectivity was obtained by addition of the aryllithium intermediate 18b to the acylimine 17a to yield the diastereomeric addition products 19c / 20c in a ratio of 72:28. After separation, the main diastereomer 19c was cyclized to afford the dihydroisoquinoline ( R )‐ 21 , which was then hydrogenated to give the NMDA antagonistic 1‐phenyl‐1,2,3,4‐tetrahydroisoquinoline ( R )‐ 2 . The chiral auxiliary, the diol 9b , cleaved during the cylization of 19c , could be recovered in 89% yield.