Catalyst‐Dependent Divergent Synthesis of Pyrroles from 3‐Alkynyl Imine Derivatives: A Noncarbonylative and Carbonylative Approach

Abstract

A novel Ru(0)- and Rh(I)-catalyzed noncarbonylative and carbonylative cycloisomerization of readily available 3-alkynyl imine derivatives has been developed to provide 3,4-fused or nonfused pyrrole derivatives efficiently in moderate to excellent yields. The key steps involve the formation of a ruthenium carbenoid intermediate or a rhodacycle intermediate, respectively. In these reactions, CO can serve as a ligand or a reagent.

Pentannulation of Heterocycles by Virtue of Precious Metal Catalysis

“…Moreover,d ifferent substituents couldb ei ntroduced on Rhodium-catalyzed carbonylative cycloisomerization/ring expansion was exploited in the synthesis of cyclopentanonefused pyrroles 148 (Scheme 50). [68] As the beginning of the catalytic cycle, the authors proposed the formation of rhodacyclobutane 149 via oxidative addition of Rh I .I ntramolecular nucleophilic attack of the imine to the activateda lkyne andt he subsequent ring expansiong ave 150 which, after carbonylation, underwent reductivee limination to afford the product and regenerated the Rh I species.…”

“…Cyclopenta-fused pyrroled erivative 169 was prepared through Ru-catalyzedn on-carbonylative pyrrole cycloisomerization/ring expansion from cyclobutane-tethered 3-alkynyl imine 168 (Scheme 57). [68] Nucleophilic attack of imine to the ruthenium-activated alkyne generates intermediate 170 which, after ring expansion,g ave the product and regenerated the catalyst.…”

Synthesis of furans and pyrroles via migratory and double migratory cycloisomerization reactions of homopropargylic aldehydes and imines

“…2). 9 Recently, Zhang disclosed a divergent reactivity of ketones 5 in the presence of gold catalysts, where a selective 1,2-alkyl migration to the neighboring carbon affords dihydrofurans 6 or furans 7 (eq. 3).…”

Preliminaries

“…The second part of the symbol refers to the reaction type. Four types are distinguished: addition (8), rearrangement (1), exchange (6), and elimination (7), e.g. The last part of the symbol refers to the essential bond broken or, in the case of exchange reactions and eliminations, to a characteristic fragment which is lost.…”

“…In N-heterocyclic synthesis, the source of many drugs, the following catch the eye: a pyrrole synthesis from N-(2-pyridyl)ketimines and acetylene derivs. via palladium-catalyzed oxidative directed C(sp 3 )-H bond activation 6 ; a samarium(III)-catalyzed synthesis of 1,2,4-trisubstituted imidazoles from 2-acetylene-sec-amines and nitriles 7 ; a metal-free synthesis of 3-aroylindoles from tertiary o-(arylethynyl)anilines using Bu 4 NI as catalyst and t-BuOOH as oxidant via geminal C(sp 3 )-H bond activation 8 ; an N-alkylative ring closure of β-amino-α-diazo-esters to 1,2,3-triazoline-4-carboxylic acid esters, and Au-catalyzed conversion of propargyl-derivatives to pyrroles 9 ; the conversion of α-diazo-γ,δ-ethylene-β-ketoalkoximes to either pyridine-3-carboxylic acid esters under rhodium catalysis or pyrrole-3-carboxylic acid esters (cf. 81, 494) under nickel catalysis 10 ; a palladium-catalyzed double carbonylation of o-dibromides to give N-substituted phthalimides, including application to the syntheis of the controversial drug, thalidomide 11 ; a triphenylphosphinecatalyzed synthesis of N-tosyl-4(1H)-quinolone-3-carbonyl compounds from o-(tosylamino)thiolic acid aryl esters and electron-deficient acetylene derivatives 12 ; a regioselective rhodium-catalyzed route to 3-alkyl-substituted isoquinolines from aryl O-pivaloyloximes and 1,3-dienes under mild, redoxneutral conditions 13 ; an organocatalyzed oxidative annelation of arylhydroxamic acid esters with acetylene derivatives to afford N-alkoxyisocarbostyrils using simple reagents, such as iodobenzene and peroxyacetic acid 14 ; and an unprecedented oxidative rearrangement of 2,2′-diamino-1,1′-binaphthyls [BINAMS] to U-shaped azaacenes via C-C bond cleavage and nitrogen migration 15 .…”