Selenocyclisations of homoallylic sulfonamides: stereoselective methods for the elaboration of substituted pyrrolidines, pyrrolines and derivatives

Copper‐Catalyzed Domino Homologation and Cycloisomerization Reactions for 3‐Pyrroline Synthesis

“…2‐Ethyl‐5‐phenyl‐1‐tosyl‐3‐pyrroline (6c): 23 The reaction of 1l (50 mg, 0.18 mmol), CuBr (10 mg, 0.07 mmol), propanaldehyde (0.03 mL, 0.36 mmol), and di‐ n ‐propylamine (0.05 mL, 0.36 mmol) in dioxane (1.2 mL) afforded 6c (15 mg, 34 %) as a mixture of cis ‐ 6c and trans ‐ 6c (1.3:1), after column chromatography (hexane/EtOAc, 20:1). For cis ‐ 6c , 1 H NMR (300 MHz, CDCl 3 ): δ = 7.64 (d, J = 8.4 Hz, 2 H), 7.33 (d, J = 8 Hz, 2 H), 5.76 (dq, J = 5.2, 1.3 Hz, 1 H), 5.64 (dq, J = 5.2, 1.3 Hz, 1 H), 5.47 (d, J = 2.2 Hz, 1 H), 4.49–4.45 (m, 1 H), 2.40 (s, 3 H), 2.04–1.98 (m, 1 H), 1.73–1.63 (m, 1 H), 0.97 (t, J = 7.5 Hz, 3 H) ppm.…”

Recent advances in selenium promoted or catalyzed electrophilic aminations of alkenes and alkynes

“…Common substrates are alkenes bearing electron-deficient nitrogen containing functional groups such as amides, carbamates, and sulfonamides. [41][42][43][44][45][46][47] The nucleophilicity of sp 2 hybridized nitrogen atoms is sufficient to intramolecularly trap the seleniranium intermediates. In fact, several ring forming reactions were performed with unsaturated imidates, imines and its derivatives such as oximes and hydrazones.…”

Piperidines from acid-catalysed cyclisations: Pitfalls, solutions and a new ring contraction to pyrrolidines

“…The products, 14 and 15, could be separated by column chromatography and were fully characterized. 8,9 There was clearly only a very narrow window of opportunity available for the formation of piperidine 14 and then only as a major product. Significantly, when a separated sample of the latter was re-exposed to the acidic conditions, it was rapidly converted into the pyrrolidine 15, indicating that it was a genuine intermedi-ate between the precursor 13 and pyrrolidine 15.…”