Scheme 2. Transformation of aldol product 8. Reagents and conditions: (a) 3d (15 mol%), CH₂Cl₂, 4 Å MS, –50 °C; (b) PPTS, DHP, CH₂Cl₂, rt; then K₂CO₃, Na₂SO₄, MeOH, rt; (c) 2 N HCl, MeOH, rt; (d) HCl in MeOH (∼1.25 M), rt; (e) SOCl₂, THF, rt; (f) 2 N HCl, THF, rt; (g) 3e (15 mol%), CH₂Cl₂, 4 Å MS, –50 °C. PPTS = pyridinum-p-toluenesulfonate; DHP = 3,4-dihydro-2-H-pyran.