Total Synthesis of Uleine-Type and Strychnos Alkaloids through a Common Intermediate
摘要:
A stereoselective total synthesis of the alkaloids of the uleine group, dasycarpidone, dasycarpidol, and nordasycarpidone, has been accomplished from the tetracyclic intermediate 1, which has been prepared by two alternative routes, either by Fischer indolization of 2-azabicyclo[3.3.1]nonanone 9 or, more efficiently, by stereocontrolled cyclization of 2-[(2-cyano-3-ethyl-4-piperidyl)methyl]i 24a and 24b. From the same tetracyclic intermediate 1, the Strychnos alkaloid tubotaiwine was also synthesized, the key step being the construction of the quaternary spiranic center by cyclization of a thionium ion upon the indole beta-position.
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.
The hexahydro-1,5-methanoazocino[4,3-b]indole (2a) was converted into (±)-tubifolidine (6a)via a four-step synthetic sequence which involves cyclization of a thionium ion upon the 3-position of a 2,3-disubstituted indole as the crucial step.
通过四步合成序列将六氢-1,5-甲亚氮并吲哚并[4,3- b ]吲哚(2a)转化为(±)-tubifolidine(6a),该过程涉及在硫醇离子的3位上环化硫鎓离子。 2,3-二取代的吲哚是关键步骤。
Enantiopure intermediates for the synthesis of Strychnos alkaloids
作者:Mercedes Amat、Ma Dolors Coll、Joan Bosch
DOI:10.1016/0040-4020(95)00641-k
日期:1995.9
The addition of 2-(lithiomethyl)indole 2 to the enantiopure oxazolinylpyridine 18 followed by acidic treatment afforded a mixture of tetracyclic compounds 21a and 21b in a 3:2 ratio. The major epimer 21a was converted to tetracycle 25a, a tetracyclic ABDE substructure of Strychnos alkaloids.
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.
Total Synthesis of Uleine-Type and Strychnos Alkaloids through a Common Intermediate
A stereoselective total synthesis of the alkaloids of the uleine group, dasycarpidone, dasycarpidol, and nordasycarpidone, has been accomplished from the tetracyclic intermediate 1, which has been prepared by two alternative routes, either by Fischer indolization of 2-azabicyclo[3.3.1]nonanone 9 or, more efficiently, by stereocontrolled cyclization of 2-[(2-cyano-3-ethyl-4-piperidyl)methyl]i 24a and 24b. From the same tetracyclic intermediate 1, the Strychnos alkaloid tubotaiwine was also synthesized, the key step being the construction of the quaternary spiranic center by cyclization of a thionium ion upon the indole beta-position.