Chiral Dipole-Stabilized Anions: Experiment and Theory in Benzylic and Allylic Systems. Stereoselective Deprotonations, Pyramidal Inversions, and Stereoselective Alkylations of Lithiated (Tetrahydroisoquinolyl)oxazolines

Article abstract of DOI:10.1021/ja00188a040

The stereoselective alkylation of chiral (tetrahydroisoquinolyl)oxazolines has been investigated.We report the details of this investigation, including an examination of the effect of both temperature and oxazoline substituent structure on the alkylation diastereoselectivity, a comparison of monodentate vs bidentate chelation of the organolithium, an evaluation of the effect of solvent and chelating solvent additives, the regiochemistry of alkylation of (3,4-dehydropiperidino)oxazolines, lithiation-alkylation experiments on stereoselectively deuterated monodentate and bidentate isoquinolinolyloxazolines, and semiempirical molecular orbital calculations on the organolithium diastereomers 13a,b.There are two distinct stereoselective processes involved in the overall transformation. the proposed mechanism includes an oxazoline-alkyllithium coordination complex that controls the selectivity of the deprotonation step, whereas the selectivity of the electrophilic quench is governed by effects that are as yet undetermined.