Studies on the synthesis of Strychnos alkaloids. A new entry into the azocino[4,3-b]indole core structure and related studies
摘要:
Treatment of cyclohexanone-3-acetic acid with phenylhydrazine hydrochloride gave the tetrahydrocarbazole 7 (73%). The derived methyl ester 8 (99.6%) was oxidized to the 4-oxo compound 9 in 85% yield by treatment with DDQ/90% aqueous THF at 0-degrees-C. Treatment of 9 with NaH/DMF at 0-degrees-C followed by (p-methoxyphenyl)sulfonyl chloride gave 10 (81%). Hydrolysis of 10 using lithium hydroxide in aqueous THF gave the acid 11 (86%). The acid 11 was converted into the amide 12 by treatment with ethylchloroformate/NEt3/CH2Cl2 followed by aqueous NH4OH. The ketoamide 12 was exposed to NaBH4/MeOH/THF to give a single alcohol 13 (> 95%). Exposure of 13 to trifluoroacetic acid (cat)/CH2Cl2/0-20-degrees-C gave the azocino[4.3-b]indole core tetracyclic lactam 14 (90%). The amide 14 was reduced (BH3.THF) to give 21, which was directly acetylated (PhSCH2COCl) to give exocyclic amide 22. All attempts to close the C11-C12 bond only resulted in decomposition. Treatment of the acid 11 with EtO2CCl/Et3N followed by [2-(phenylthio)ethyl]amine gave the amide 24 (90%). Reduction of 24 using NaBH4 gave the alcohol 25 which upon exposure to CF3CO2H at room temperature cyclized to the tetracyclic amide 26 (96% overall). Oxidation of the sulfide 26 (m-CPBA) resulted in the diastereomeric sulfoxides 28. When the sulfoxides 28 were exposed to Pummerer conditions the only products that could be isolated were the (E)- and (Z)-vinyl sulfides 29 (72% and 25%, respectively). Similarly the dimethylthio acetal 33 was converted into the aldehyde 34 (100%). Treatment of 26 with POCl3/DMF gave 35 (90.8%) which was exposed to PhNHNH2/AcOH/AcONa to give the pyrazole 36 (85%). Attempts to close the E-ring via sulfoxides derived from either the pyrazole 36 or the oxazole 37 were unsuccessful. Treatment of the chloride 40 with KH/HN(SiMe3)2 in toluene resulted in a slow conversion into the 3-oxindole 44.
Studies on the synthesis of Strychnos alkaloids. A new entry into the azocino[4,3-b]indole core structure and related studies
作者:Philip Magnus、Nancy L. Sear、Chung S. Kim、Nigel Vicker
DOI:10.1021/jo00027a016
日期:1992.1
Treatment of cyclohexanone-3-acetic acid with phenylhydrazine hydrochloride gave the tetrahydrocarbazole 7 (73%). The derived methyl ester 8 (99.6%) was oxidized to the 4-oxo compound 9 in 85% yield by treatment with DDQ/90% aqueous THF at 0-degrees-C. Treatment of 9 with NaH/DMF at 0-degrees-C followed by (p-methoxyphenyl)sulfonyl chloride gave 10 (81%). Hydrolysis of 10 using lithium hydroxide in aqueous THF gave the acid 11 (86%). The acid 11 was converted into the amide 12 by treatment with ethylchloroformate/NEt3/CH2Cl2 followed by aqueous NH4OH. The ketoamide 12 was exposed to NaBH4/MeOH/THF to give a single alcohol 13 (> 95%). Exposure of 13 to trifluoroacetic acid (cat)/CH2Cl2/0-20-degrees-C gave the azocino[4.3-b]indole core tetracyclic lactam 14 (90%). The amide 14 was reduced (BH3.THF) to give 21, which was directly acetylated (PhSCH2COCl) to give exocyclic amide 22. All attempts to close the C11-C12 bond only resulted in decomposition. Treatment of the acid 11 with EtO2CCl/Et3N followed by [2-(phenylthio)ethyl]amine gave the amide 24 (90%). Reduction of 24 using NaBH4 gave the alcohol 25 which upon exposure to CF3CO2H at room temperature cyclized to the tetracyclic amide 26 (96% overall). Oxidation of the sulfide 26 (m-CPBA) resulted in the diastereomeric sulfoxides 28. When the sulfoxides 28 were exposed to Pummerer conditions the only products that could be isolated were the (E)- and (Z)-vinyl sulfides 29 (72% and 25%, respectively). Similarly the dimethylthio acetal 33 was converted into the aldehyde 34 (100%). Treatment of 26 with POCl3/DMF gave 35 (90.8%) which was exposed to PhNHNH2/AcOH/AcONa to give the pyrazole 36 (85%). Attempts to close the E-ring via sulfoxides derived from either the pyrazole 36 or the oxazole 37 were unsuccessful. Treatment of the chloride 40 with KH/HN(SiMe3)2 in toluene resulted in a slow conversion into the 3-oxindole 44.