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Diastereoselectivity in the Allylation of N ‐Trialkylsilylimines of O ‐Protected (2 S )‐Lactal − Some Unexpected Results
Author(s) -
Cainelli Gianfranco,
Giacomini Daria,
Galletti Paola,
Quintavalla Arianna
Publication year - 2002
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 - 10.1002/1099-0690(200209)2002:18<3153::aid-ejoc3153>3.0.co;2-d
Subject(s) - chemistry , diastereomer , stereoselectivity , alkyl , silylation , stereochemistry , protecting group , solvation , medicinal chemistry , organic chemistry , molecule , catalysis
A comparison of the diastereoselective addition of allylMgCl to differently O ‐protected N ‐trialkylsilyllactaldimine and to N ‐benzyllactaldimines is reported. The stereoselectivity strongly depends on the O ‐ and N ‐protecting groups, on the metal cation, and on the reaction temperature, and varies from predominance of the anti diastereoisomer to predominance of the syn one. O ‐TBS‐ and O ‐TIPS‐silyl imines displayed better anti diastereoselectivity than their O ‐alkyl counterparts. The N ‐protection produced unexpected results: in particular, the bulky, achiral, N ‐TIPS group favoured the predominance of the syn diastereoisomer. The temperature dependence of the stereochemical outcome provides evidence of the important role of differential entropies of activation (ΔΔ S ≠ ), and the presence of inversion temperatures ( T inv ) related to dynamic solvation phenomena. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)