Studies on Acetylenic Compounds. XLIX. Reactions of Linear-Conjugated Diynones

Abstract

Linear conjugated diynones, capillin (Ia), and the ethyl analogue, 1-phenyl-2, 4-heptadiyn-1-one (Ib), were applied to the synthesis of the corresponding β-triketones, 1-phenyl-1, 3, 5-hexanetrione (IIIa) and 1-phenyl-1, 3, 5-heptanetrione (IIIb), respectively. Acid catalyzed hydration of Ia and Ib afforded 2-methyl-6-phenyl-4H-pyran-4-one (IIa), and 2-ethyl-6-phenyl-4H-pyran-4-one (IIb), which were converted to IIIa and IIIb by alkaline hydrolysis, respectively. On the other hand, treatment of Ia and Ib with pyrrolidine gave novel biphenyl derivatives, 3, 5-di-N-pyrrolidinyl-1, 1'-biphenyl (VIIa) and 2-methyl-3, 5-di-N-pyrrolidinyl-1, 1'-biphenyl (VIIb), in addition to normal enamine products, 1-phenyl-5-N-pyrrolidinyl-4-hexen-2-yn-1-one (Va) and 1-phenyl-5-N-pyrrolidinyl-4-hepten-2-yn-1-one (Vb), respectively. Acid hydrolysis of Va and Vb also afforded the expected 4-pyrone derivatives (IIa, IIb). In order to examine the mechanistic pathway of I to VII, 1-phenyl-5-N-pyrrolidinyl-4-hexen-1, 3-dione (IX) derived from IIIa was treated with pyrrolidine to lead to VIIa, which was assumed to form the same intermediate (VI).