δ-Quaternary Amino Acids and Dihydroisoquinolones from the Addition of Laterally Lithiated Aryl Carboxylates to <i>N</i> -Sulfinyl Ketimines

Lateral lithiation of aryl and heteroaryl 2-methyl carboxylic acids with LDA and subsequent addition of the dianions to <i>N</i>-<i>tert</i>-butanesulfinyl ketimines gives <i>N</i>-sulfinyl δ-amino acids with high diastereoselectivities. One-pot sulfinyl deprotection and cyclization yield 3,3-disubstituted 3,4-dihydroisoquinolones and related heterocycles. <i>tert</i>-Butanesulfinyl chloride generated during the deprotection was shown to be an efficient reagent for intra- and intermolecular amide bond formation. This process gives access to δ-amino acids and 3,4-dihydroisoquinolones bearing a quaternary stereocenter that is not readily prepared by existing methods.