Abstract
The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (N-PMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine. In particular, we show that under kinetic control (-70 °C) the additions involving electron-rich N-arylidene groups occur with very high stereocontrol in favor of the (2S,RS)-diastereomers, whereas an electron-deficient group favors the opposite stereochemical outcome. Based on the observations above, a mechanistic hypothesis is proposed.
Highlights
The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine
Additions of chiral lithium sulfoxides to imines represent a powerful tool in asymmetric synthesis [1]
We have recently reported that kinetically controlled additions (-70 °C) of lithium methyl p-tolyl sulfoxide (2) (Scheme 1) to N-PMP(imines) (PMP = p-methoxyphenyl) derived from a series of aromatic aldehydes having a variable degree of fluorination occur with a progressively higher stereocontrol in favor of (2S,RS)-β-aminosulfoxides 3 with decreasing the number of fluorine atoms on the N-arylidene groups [2]
Summary
Additions of chiral lithium sulfoxides to imines represent a powerful tool in asymmetric synthesis [1]. Abstract: The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (NPMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine.
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