Rh(iii)-catalyzed, hydrazine-directed C–H functionalization with 1-alkynylcyclobutanols: a new strategy for 1H-indazoles

Abstract

<p>Rh(<sc>iii</sc>)-catalyzed coupling of phenylhydrazines with 1-alkynylcyclobutanols was realized through a hydrazine-directed C–H functionalization and [4+1] annulation pathway.</p>

Rh(III)‐Catalyzed C−H Activation/Annulation of N‐Methyl Arylhydrazines with Iodonium Ylides toward Ring‐fused Cinnolines

“…Based on the experimental results and previous reports, [10–12,14] a possible mechanism was proposed and listed in Scheme 3 with 1 a and 2 a as the model reactants. Firstly, the reaction between [RhCp*Cl 2 ] 2 and NaOAc gives the reactive Rh(III) species A .…”

“…They also achieved the synthesis of cinnoline scaffold via the rhodium‐catalyzed intermolecular cyclization of arylhydrazines with α‐diazo‐β‐ketoesters (Scheme 1b) [11] . More recently, Yu's group developed a Rh(III)‐catalyzed coupling of phenylhydrazines with 1‐alkynylcyclobutanols for the preparation of 1 H ‐indazoles under mild reaction conditions (Scheme 1c) [12] . In the latter two cases, the N−N bond remained intact and the retained amino group was further transformed into the binitrogen‐containing heterocycles after cyclization.…”

“…Based on the experimental results and previous reports, [10][11][12]14] a possible mechanism was proposed and listed in Scheme 3 with 1 a and 2 a as the model reactants. The application potentials of this synthetic protocol were further demonstrated in Scheme 4.…”

“…[11] More recently, Yu's group developed a Rh(III)-catalyzed coupling of phenylhydrazines with 1-alkynylcyclobutanols for the preparation of 1Hindazoles under mild reaction conditions (Scheme 1c). [12] In the latter two cases, the NÀ N bond remained intact and the retained amino group was further transformed into the binitrogen-containing heterocycles after cyclization. Additionally, as an efficient carbene precursor, iodonium ylides exhibit good thermal stability and have been widely employed to construct various useful structures under catalyst-free conditions or catalyzed by transition metals.…”

Synthesis of Indolyl-Tethered Spiro[cyclobutane-1,1′-indenes] through Cascade Reactions of 1-(Pyridin-2-yl)-1H-indoles with Alkynyl Cyclobutanols

“…Inspired by the elegant pioneering studies of TM-catalyzed addition of C­(sp 2 )–H bonds to alkynes, we have recently established an efficient and selective synthesis of 2-acylindoles and pyrazolo­[1,2- a ]­pyrazolones from the sequential reaction of 1-phenylpyrazolidinones with alkynyl cyclobutanols via cascade cleavage of C–H, N–H, C–C, and N–N bonds along with cyclobutanol ring opening (Scheme a) . As a continuation of our interest in developing new synthetic approaches toward rare or unknown organic scaffolds by taking advantage of C–H bond functionalization methodologies, , we have designed and explored the reaction between 1-(pyridin-2-yl)-1 H -indole and alkynyl cyclobutanol . It was initially envisioned by us that 1-(pyridin-2-yl)-1 H -indole would undergo a C2­(sp 2 )–H alkenylation with the triple bond of alkynyl cyclobutanol.…”