Lewis base dependent (3+3) annulations of β′/δ-acetoxy allenoates with iminoindolines offer α-carbolines with varying substituents depending on the base used as well as subtle changes in the reaction conditions. The phosphine-catalyzed annulation of δ-acetoxy allenoates with iminoindolines involves 6-exo-trig cyclization, tosyl anion elimination/trapping, and ethyl acetate elimination as key steps in delivering β-H and γ-tosyl containing α-carbolines. An unobvious elimination (by C_α-C_β bond cleavage) of the −CH₂CO₂Et moiety is observed here. The same reactants under DBU catalysis offer α-carbolines that retain −CH₂CO₂Et moiety but are devoid of −Ts group via 6-exo-dig cyclization. The reaction of β′-acetoxy allenoate with iminoindolines is completely tertiary amine dependent; the use of DABCO affords tetrahydro-α-carbolines exclusively with excellent stereoselectivity while DBU offers substituted α-carbolines that are distinct from those using DABCO. Several control experiments and HRMS studies have been done in support of a plausible reaction mechanism.

中文翻译：

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乙酰氧基联烯酸酯与亚氨基二氢吲哚的路易斯碱相关 (3+3) 环化：具有不同取代基的 α-咔啉支架

β' / δ-乙酰氧基联烯酸酯与亚氨基二氢吲哚的路易斯碱依赖性 (3+3) 环化提供具有不同取代基的α-咔啉，这取决于所用的碱以及反应条件的细微变化。膦催化的δ-乙酰氧基联烯酸与亚氨基二氢吲哚的环化涉及 6-外三角环化、甲苯磺酰基阴离子消除/捕获和乙酸乙酯消除作为传递含有α-咔啉的β -H 和γ -甲苯磺酰基的关键步骤。-CH ₂ CO ₂的不明显消除（通过 C _α -C _{β键断裂）}此处观察到 Et 部分。在 DBU 催化下，相同的反应物通过6-exo-dig环化提供保留了 -CH ₂ CO ₂ Et 部分但没有 -Ts 基团的α -咔啉。β'-乙酰氧基联烯酸酯与亚氨基二氢吲哚的反应完全依赖于叔胺；DABCO 的使用为四氢-α-咔啉提供了独有的出色立体选择性，而 DBU 提供了取代的α-咔啉，这与使用 DABCO 的那些不同。已经进行了几项控制实验和 HRMS 研究以支持合理的反应机制。