A mixture of 300 g dihydropyridine of Step 1 and 2 g freshly sublimed sulfur in 100 ml xylene was heated to 200°-210° C. for 30 minutes. When the development of hydrogen sulfide had subsided, the reaction mixture was cooled to room temperature, and ca. 100 g of Charcoal plus 1000 ml of ethyl acetate was added. This mixture was heated to reflux for 6 hours and then filtered through Celite filter aid. The filtrate was concentrated under vacuum and the residue was chromatographed on silica-gel, eluting with ethyl acetate/hexane to yield 78 g of the Step 2 title product.
