Abstract
The alkylidene 1,3‐dioxo compounds 4a–d with an allylsilane moiety undergo a fluoride‐, Lewis acid‐ and TMSOTf‐induced intramolecular cyclisation to give almost exclusively the trans‐1,2‐disubstituted cyclopentanes 5a–d in good to excellent yields. The diastereoselectivity of the reaction was determined as a function of the 1,3‐dioxo moiety and the inductor. The best results were obtained with FeCl3/Al2O3 followed by TMSOTf and Me2AlCl1 the highest selectivity was found in the cyclisation of 4b with TMSOTf leading to 5b and 6b in a ratio of 99.8:0.2. FeCl3/Al2O3 and TMSOTf have not previously been used for this type of reaction. The alkylidene 1,3‐dioxo compounds 4a–d were synthesised by Knoevenagel condensation of the aldehyde 11 with the malonic acid derivatives 11a–d.

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