Reaction of enamino-phosphonium salts derived from β-aminoacids with α,β-unsaturated aldehydes leads to the formation of symmetrical dihydropyridines. Moreover, no symmetrical dihydropyridines can be obtained by the reaction of enamino-phosphonium salts derived from of N-vinylic phosphazenes with α,β-unsaturated ketones. Results and Discussion Reaction of enamino-phosphonium salts 3 with α,β-unsaturated aldehydes 2. Preparation of symmetrical dihydropyridines 5 and pyridine 6 We explored the

more »

... ctivity of enaminophosphonium salts 3 derived from phosphazenes 1 with α,β-unsaturated aldehydes 2 (Scheme 2). The reaction of enaminophosphonium salt 3a, prepared by hydrochloric acid treatment of N-vinylic phosphazene 1a (R 1 = H, R 2 = Et), with cinnamaldehyde 2a (R 3 = C 6 H 5 ) or p-nitrocinnamaldehyde 2b (R 3 = 4-NO 2 -C 6 H 4 ) in refluxing CH 2 Cl 2 led to the formation of 4-(2-phenylethenyl)-3,5-diethoxycarbonyl-1,4-dihydropyridine