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Reversed Stereochemical Course of the Michael Addition of Cyclohexanone to β‐Nitrostyrenes by Using 1‐(Trimethylsiloxy)cyclohexene/Dichloro(diisopropoxy)titanium. Preliminary Communication
Author(s) -
Seebach Dieter,
Brook Michael A.
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680205
Subject(s) - chemistry , cyclohexanone , diastereomer , bicyclic molecule , nitronate , cyclohexene , lewis acids and bases , medicinal chemistry , acetal , aryl , chiral auxiliary , organic chemistry , stereochemistry , catalysis , enantioselective synthesis , nitro , alkyl
Induced by a stoichiometric excess of dichloro(diisopropoxy)titanium, 1‐(trimethylsiloxy)cyclohexene and p ‐substituted β‐nitrostyrenes (Y = H,CH 3 ,CH 3 O,CN) combine in CH 2 Cl 2 solution at −90° preferentially with relative topicity ul – opposite to the corresponding reaction of enolates or enamines. The primary products are the bicyclic nitronates 3–5 which can be separated, and which are cleaved by KF in MeOH to give the aryl(nitroethyl)‐substituted cyclohexanones 1 and 2 ( Tables 1 and 2 , two typical procedures are given). The major products (2:1 to 4:1) are the hitherto not readily available diastereoisomers 2 of l ‐configuration. Instead of being solvolyzed, the bicyclic nitronate 5 can be used for nitroaldol additions (→ 6 ) and for [3 + 2]‐dipolar cycloadditions (→ 7 ), diastereoselectively furnishing products with 4 asymmetric C‐atoms (not counting acetal centers). The Michael addition described here is yet another example of an ul ‐combination of trigonal centers induced by Lewis acids, overriding the influence of the configuration of the donor component.