A new synthetic entry to pentacyclic Strychnos alkaloids. Total synthesis of (.+-.)-tubifolidine, (.+-.)-tubifoline, and (.+-.)-19,20-dihydroakuammicine
摘要:
A new strategy for the synthesis of pentacyclic Strychnos alkaloids has been developed. It consists in the closure of the five-membered E ring by cyclization upon the indole 3-position from a suitably N-substituted tetracyclic system embodying rings ABCD of the alkaloids. Attempts to effect the key cyclization either by Pummerer rearrangement of sulfinylacetamides 4 and 6, from chloroacetamide 12, or from bis(methylthio)acetamide 10b (exocyclic amide carbonyl group) resulted in failure. In the first case dithioacetals 9 and 10, respectively, were formed in good yields. Cyclization from alcohol 13 or from the indole-deactivated acetal 15 and dithiocetal 18 were also unsuccessful: noncyclized products coming from the initially formed oxonium or thionium intermediates 16 were obtained. Cyclization was satisfactorily accomplished in 49% yield by treatment of the N-unsubstituted indole dithioacetal 23 with DMTSF. The resulting pentacycle 25 was converted to 20-deethyltubifolidine (27). A similar treatment from dithioacetal 41a, prepared from the secondary amine 32a, afforded pentacycle 42a, from which the alkaloids tubifoline, tubifolidine, and 19,20-dihydroakuammicine were synthesized.
A new synthetic entry to pentacyclic Strychnos alkaloids. Total synthesis of (.+-.)-tubifolidine, (.+-.)-tubifoline, and (.+-.)-19,20-dihydroakuammicine
摘要:
A new strategy for the synthesis of pentacyclic Strychnos alkaloids has been developed. It consists in the closure of the five-membered E ring by cyclization upon the indole 3-position from a suitably N-substituted tetracyclic system embodying rings ABCD of the alkaloids. Attempts to effect the key cyclization either by Pummerer rearrangement of sulfinylacetamides 4 and 6, from chloroacetamide 12, or from bis(methylthio)acetamide 10b (exocyclic amide carbonyl group) resulted in failure. In the first case dithioacetals 9 and 10, respectively, were formed in good yields. Cyclization from alcohol 13 or from the indole-deactivated acetal 15 and dithiocetal 18 were also unsuccessful: noncyclized products coming from the initially formed oxonium or thionium intermediates 16 were obtained. Cyclization was satisfactorily accomplished in 49% yield by treatment of the N-unsubstituted indole dithioacetal 23 with DMTSF. The resulting pentacycle 25 was converted to 20-deethyltubifolidine (27). A similar treatment from dithioacetal 41a, prepared from the secondary amine 32a, afforded pentacycle 42a, from which the alkaloids tubifoline, tubifolidine, and 19,20-dihydroakuammicine were synthesized.
AMAT, MERCEDES;LINARES, ANA;BOSCH, JOAN, J. ORG. CHEM., 55,(1990) N6, C. 6299-6312
作者:AMAT, MERCEDES、LINARES, ANA、BOSCH, JOAN
DOI:——
日期:——
A new synthetic entry to pentacyclic Strychnos alkaloids. Total synthesis of (.+-.)-tubifolidine, (.+-.)-tubifoline, and (.+-.)-19,20-dihydroakuammicine
作者:Mercedes Amat、Ana Linares、Joan Bosch
DOI:10.1021/jo00313a017
日期:1990.12
A new strategy for the synthesis of pentacyclic Strychnos alkaloids has been developed. It consists in the closure of the five-membered E ring by cyclization upon the indole 3-position from a suitably N-substituted tetracyclic system embodying rings ABCD of the alkaloids. Attempts to effect the key cyclization either by Pummerer rearrangement of sulfinylacetamides 4 and 6, from chloroacetamide 12, or from bis(methylthio)acetamide 10b (exocyclic amide carbonyl group) resulted in failure. In the first case dithioacetals 9 and 10, respectively, were formed in good yields. Cyclization from alcohol 13 or from the indole-deactivated acetal 15 and dithiocetal 18 were also unsuccessful: noncyclized products coming from the initially formed oxonium or thionium intermediates 16 were obtained. Cyclization was satisfactorily accomplished in 49% yield by treatment of the N-unsubstituted indole dithioacetal 23 with DMTSF. The resulting pentacycle 25 was converted to 20-deethyltubifolidine (27). A similar treatment from dithioacetal 41a, prepared from the secondary amine 32a, afforded pentacycle 42a, from which the alkaloids tubifoline, tubifolidine, and 19,20-dihydroakuammicine were synthesized.