The bicyclic lactams derived from (S)-valinol and 3-benzoylpropionic acid or levulinic acid are useful chiral precursors to the title compounds. Metalation of bicyclic lactams 1 or 4 and alkylation followed by acidic hydrolysis leads to racemic 2-alkyl carboxylic acids. However, sequential metalation-alkylation to 2, 2-dialkyl bicyclic lactams 2 and 5 furnishes these systems with good diastereoselectivity. Treatment of 5 with triflic acid causes a facile ...
