A Direct, Versatile, and Chemoselective Synthesis of Vinylogous Bis- and Monourethanes/amides and β-Keto Esters by Aza-Knoevenagel-Type Reactions of Tertiary Amides with Enolates: A Direct, Versatile, and Chemoselective Synthesis of Vinylogous Bis- and Monourethanes/amides and β-Keto Esters by Aza-Knoevenagel-Type Reactions of T