Catalytic Access to Bridged Sila-N-heterocycles from Piperidines via Cascade sp³ and sp² C–Si Bond Formation

Abstract

Described herein is the development of an unprecedented route to bridged sila-N-heterocycles via B­(C6F5)3-catalyzed cascade silylation of N-aryl piperidines with hydrosilanes. Mechanistic studies indicated that an outer-sphere ionic path is operative to involve three sequential catalytic steps having N-silyl piperidinium borohydride as a resting species: (i) dehydrogenation of the piperidine ring, (ii) β-selective hydrosilylation of a resultant enamine intermediate, and (iii) intramolecular dehydrogenative sp2 C–H silylation.

Exhaustive Reduction of Esters Enabled by Nickel Catalysis

“…15 Characterization data matched those previously reported. 28 Characterization data matched those previously reported. 31 1,3-Dimethylindole (27) was prepared according to general procedure A. Purification was performed using a gradient of 1→5% EtOAc in hexanes to afford (27) as colorless liquid (16 mg, 53% yield).…”

“…In many classical heterocycle-forming reactions, ester-containing starting materials like malonates or propiolates are used to facilitate cyclizations, thus making the ester-containing products more accessible than the corresponding methyl analogs. With this in mind, we were excited to see that many heterocycles were tolerated, including pyridines (16)(17)(18)(19)(20), morpholines (21,22), piperidines (23,24), indoles (25)(26)(27)(28)(29), carbazoles (30)(31)(32), an indazole (33), quinoline (34), benzofuran (35), and dibenzofuran (36). Derivatization of commercial pharmaceuticals bifendatatum and probenecid successfully formed reduction products 37 and 38, respectively.…”

Comparative DFT study of metal-free Lewis acid-catalyzed C–H and N–H silylation of (hetero)arenes: mechanistic studies and expansion of catalyst and substrate scope

“…Since then, C-H silylations of thiophenes, pyridines, indoles and anilines with hydrosilanes using Lewis acid B(C 6 F 5 ) 3 , Al(C 6 F 5 ) 3 or Brønsted acid [H(OEt 2 ) 2 ] + [B(C 6 F 5 ) 4 ] À as the catalysts have been reported (Scheme 1(a and b)). [8][9][10][11][12][13] Furthermore, N-H silylations of aniline with hydrosilanes catalyzed by B(C 6 F 5 ) 3 and [(C 6 F 5 ) 3 PF][B(C 6 F 5 ) 4 ] were observed by the Paradies and Stephan groups (Scheme 1(c)). 14 Although many catalytic cycles for the silylation of aromatic C-H bonds using hydrosilanes have been proposed in previous experimental studies, few mechanistic investigations have been performed.…”

Metal-free C(sp3)–H functionalization of sulfonamidesviastrain-release rearrangement

“…In contrast, transition metalfree protocols are greatly rare in this field. In 2014, Seidel have reported a redox-neutral α,β-difunctionalization cascade reaction of cyclic amines under microwave irradiation at 200 o C. 13 In 2018, Chang presented a B(C 6 F 5 ) 3 -catalyzed β-C-H silylation of N-aryl piperidines with hydrosilanes at 120 o C. 14 Notably, Seidel used organolithium reagents to achieve multi-C-H functionalization of alicyclic amines. And a key intermediate, situ-generated endocyclic 1-azaallyl anion, was proposed in this report.…”