Synthesis of 20-deethylsilicine from a second-generation 2-cyano-.DELTA.3-piperidine synthon

The Zn 2 + catalyzed reaction of the 2-cyano-Δ 3 -piperidine (9a X = SO 2 C 6 H 5 and 9b X =CN ) with indole gave the C-7 indole-substituted aminonitriles 37a,b and 38, respectively. These intermediates were converted to Δ 2 -piperidine 40 on reaction with sodium dimethyl malonate and AgBF 4 . Stereoselective hydrogenation of the enamine doyble bond in 40 furnished the required cis 3,4-disubstituted piperidine 41, which was cyclized under acidic conditions to the target molecule, 20-deethylsilicine (20).