Studies on indenopyridine derivatives and related compounds. VI Synthesis and stereochemistry of ethyl 9,9-dimethyl-1,2,3,9a-tetrahydro-9H-indeno(2,1-b)pyridine-3-carboxylate as a possible intermediate for the total synthesis of lysergic acid.
作者:TAKUSHI KURIHARA、TATSUYA TERADA、SHIGEYO SATODA、RYUJI YONEDA
DOI:10.1248/cpb.34.2786
日期:——
Reaction of 1, 1-dimethylindene-3-carbonyl chloride (9), prepared from 3, 3-dimethylindanone (5) via a four step sequence, with ethyl 3-(N-tert-butoxycarbonyl-N-methyl)aminopropionate (14)or its 2-methyl derivative (15) in the presence of lithium diisopropylamide (LDA) gave the β-keto esters (16 and 17). De-tert-butoxycarbonylation of 16 followed by treatment with sodium bicarbonate did not give 12, while 17 afforded the cyclized β-keto ester (19) in good yield. Sodium borohydride reduction of 19 followed by treatment with methanesulfonyl chloride gave the mesylate (21), which was reacted with 1, 8-diazabicyclo[5.4.0]-7-undecene (DBU) to give the unsaturated ester (22). By analogous reaction sequences, the diethylamide derivative (2) was synthesized in moderate yield. Reaction of the β-keto ester (16) with diethyl phosphorochloridate in the presence of LDA gave the enolphosphate (30), which was converted to the unsaturated esters (31a and 31b) in good yields. However, dephosphorylation of 31 failed. Sodium borohydride reduction of 16 gave the alcohol (33), which was converted to the diene ester (34) or the mesylate (36). These were successfully converted to the ethyl 1, 2, 3, 9a-tetrahydro-9H-indeno[2, 1-b]pyridine-3-carboxylates (32s and 32b), which were found to exist in an equilibrium mixture, in excellent yields, respectively. The stereochemistry of some of the key intermediates and of the target compounds is discussed.
1,1-二甲基茴香烯-3-羰基氯(9),由3,3-二甲基茴香酮(5)经过四步反应制备而成,和乙基3-(N-叔丁氧羰基-N-甲基)氨基丙酸酯(14)或者其2-甲基衍生物(15)在二异丙胺锂(LDA)存在下反应,得到β-酮酯(16和17)。16的去叔丁氧羰基化反应后,用碳酸钠处理未能得到12,而17则以良好的产率生成环化的β-酮酯(19)。对19进行硼氢化钠还原后,再与甲磺酰氯反应得到甲磺酸酯(21),该化合物与1,8-二氮杂双环[5.4.0]-7-十一烯(DBU)反应生成不饱和酯(22)。通过类似的反应序列,二乙酰胺衍生物(2)以中等产率合成。β-酮酯(16)与二乙基氯磷酸酯在LDA存在下反应得到烯酯磷酸酯(30),再转化为不饱和酯(31a和31b),产率良好。然而,31的去磷酸化反应失败。对16进行硼氢化钠还原得到醇(33),该醇可以转化为二烯酯(34)或甲磺酸酯(36)。这些化合物最终成功转化为乙基1,2,3,9a-四氢-9H-茴香[2,1-b]吡啶-3-羧酸酯(32s和32b),发现它们以良好的产率存在于平衡混合物中。部分关键中间体和目标化合物的立体化学进行了讨论。