1 SYNTHETIC STUDY ON ECHINULIN AND RELATED COMPOUNDS
Details
A stereoselective total synthesis of optically active echinulin (1) will be discussed. To establish a method synthesizing 2, 4-(γ, γ-dimethylallyl)aniline (15) required for the synthesis of the indole moiety of echinulin (1), the acid-catalyzed amino Claisen rearrangement of N-allyl- and N-(γ,γ-dimethylallyl)aniline derivatives was examined; namely,the compounds (3), (6), (8), (11), (12), and (14) were synthesized from the corresponding N-substituted aniline derivatives. By this rearrangement, N, N-di-(γ, γ-dimethylallyl)aniline (13) was converted to 2, 4-di-(γ,γ-dimethylallyl)aniline (15) in 23% yield,which was then transformed to the gramine (21) according to Saxton's method. The gramine (21) was condensed with the diketopiperazine (22) synthesized from L-alanine. After the ester thus obtained had been hydrolyzed to the acid (24), it was heated in dioxane to afford optically active echinulin (25) (two parts) and epi-echinulin (26) (one part). The synthesized echinuline (25) was identical with natural echinulin (1) in all respects (mp, mixed mp,[α]_D, ir, nmr, etc.).
