Borane-catalyzed cascade Friedel–Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization to afford tetrahydroquinolines

Abstract

An unprecedented redox-neutral annulation of tertiary anilines with electron-deficient alkynes was developed that proceeds through a cascade Friedel-Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization sequence. Under B(C6F5)3 catalysis, a range of functionalized 1,2,3,4-tetrahydroquinolines...

Aromatization-driven cascade [1,5]-hydride transfer/cyclization for synthesis of spirochromanes

“…5 A variety of heterocycles could be generated via the cascade hydride transfer/cyclization process with the breaking and formation of a number of bonds in one operation. 6 In addition, the specific mode of hydride transfer/cyclization always requires a substrate that incorporates a linker, a hydride donor and an acceptor (Scheme 1c). 5,6 In the past decade, hydride transfer reactions were well developed with the C(sp 3 )–H bond adjacent to a nitrogen atom as the hydride donor.…”

“…6 In addition, the specific mode of hydride transfer/cyclization always requires a substrate that incorporates a linker, a hydride donor and an acceptor (Scheme 1c). 5,6 In the past decade, hydride transfer reactions were well developed with the C(sp 3 )–H bond adjacent to a nitrogen atom as the hydride donor. 5,6 In contrast, hydride transfer reactions with the C(sp 3 )–H bond adjacent to an oxygen atom as the hydride donor have been relatively challenging due to the following reasons: (1) the C(sp 3 )–H bond adjacent to an oxygen atom is less reactive than the C(sp 3 )–H bond adjacent to a nitrogen atom; and (2) the in situ formed acyclic oxocarbenium intermediate is unstable and tends to undergo hydrolysis.…”

Borane-catalyzed dehydrogenative C–C bond formation of indoles with N-tosylhydrazones: an experimental and computational study

“…39–45 To date a series of boron based Lewis acid catalysts have been known in the main group chemistry, out of which tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ) has evolved as the most versatile catalyst. 46–48 The inherent electrophilic character and strong Lewis acidity have increased its applications in various transformations including cyclization, 49–53 dehydrogenation, 54–57 hydrosilylation, 58–61 hydroboration, 62,63 and Frustrated Lewis Pair (FLP) chemistry 64–68 for activation of small molecules. Most importantly, regioselective C3 alkylation of indoles by C–C bond formation that leads to omnipresent bioactive indole derivatives has recently been demonstrated in the presence of a B(C 6 F 5 ) 3 catalyst (Scheme 1).…”

Borane-catalyzed arylation of aryldiazoacetates withN,N-dialkylanilines

“…Inspired by our previous work on the B(C 6 F 5 ) 3 -catalyzed functionalization of tertiary amines, 14 we envisioned that B(C 6 F 5 ) 3 catalytic system could be able to expand methods for the synthesis of diarylacetates containing dialkylamino groups. Herein, we reported a selective arylation of aryldiazoacetates with N , N -dialkylanilines catalyzed by B(C 6 F 5 ) 3 to deliver a range of diarylacetates in good to high yields (Scheme 1c).…”