Enantioselective Metalation of N,N-Diisopropylferrocenecarboxamide and Methyl Ferrocenecarboxylate Using Lithium-Metal Chiral Bases

• Enantioselective deprotonative metalations of substituted ferrocenes using mixed lithium-metal bases are described. Using N,N-diisopropylferrocenecarboxamide as substrate, magnesium, iron, cobalt, zinc, and cadmium were tested as metals in bis[(S)-1-phenylethyl]amido-based combinations; after interception of the metalated species with iodine, very high enantiomeric excess (96?%) but low yield was obtained with cobalt, whereas zinc and cadmium only gave 27 and 30?%?ee, respectively, but in excellent yields. The small alkyl groups methyl and ethyl were identified as particularly suitable in the reaction using the putative dialkyl bis[(S)-1-phenylethyl]amido-based lithium and dilithium zincates. The dimethyl dilithium zincate was selected for a study of dependency on the temperature, reaction time, and amount of base. Increased enantioselectivities with temperature, reaction time, and amount of base were noted (ee = 86?% at 0 degrees C after 2 h, 2 equiv. of base). The best result using methyl ferrocenecarboxylate as substrate was observed without alkyl ligand.

Subject headings

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Keyword

Metalation

Chirality

Zinc

Lithium

Metallocenes

Sandwich complexes

deprotonative metalation

structural elucidation

ortho-lithiation

amide bases

ferrocenes

planar

zinc

chemistry

magnesium

nmr

ice d

1995

tetrahedron letters

v36

p6135

Publication and Content Type

ref (subject category)

art (subject category)