Abstract
Asymmetric Mannich condensations can give rise to enantiomerically
pure β-amino carbonyl functionalities, which are important
constituents of many biologically active natural products and therapeutics.
We describe the titanium tetrachloride-mediated reaction of chiral
enolates derived from thiazolidine thiones and non-enolizable imines.
For example, N -(4-methoxyphenyl)benzaldimine
(1 ) yields 2R ,3S -(anti )-products
with good selectivity, while N -benzyloxycarbonylbenzaldimine
(2 ) equilibrates and subsequently eliminates
benzyl alkoxide under the reaction conditions to produce 2R ,3R -(syn )-isocyanates with excellent selectivity.
This reversal in selectivity from anti to syn can be achieved operationally by
simply changing the group Z on the nitrogen and the reaction conditions.
Key words
diastereoselectivity - enolates - titanium - aldimines - thiazolidine-2-thiones
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This hypothesis is supported by molecular
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