Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles

Abstract

N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6-tetrahydropyrazines.

Maculatic Acids—Sex Attractant Pheromone Components of Bald‐Faced Hornets

“…Considering that the amount of analyte was insufficient to infer the olefin geometry by NMR analysis, we selected a flexible synthetic route that would provide each of the four possible stereoisomers. As depicted in Figure , a Horner–Wadsworth–Emmons mono‐olefination of 2,6‐hexanedione using tert‐ butyl‐2‐(dimethoxyphosphoryl)acetate afforded the esters 7 and 8 in 48 % combined yield, which were separable by flash column chromatography using AgNO 3 ‐impregnated silica gel. With geometrically pure 7 and 8 in hand, a subsequent Wittig reaction with the anion derived from (2‐carboxyethyl)triphenylphosphonium bromide provided a mixture of the E ‐ and Z ‐alkenes 9 and 10 .…”

Preparation of a Novel pH-responsive Fluorescent Probe Based on an Imidazo[1,2-a]indole Fluorophore and its Application in Detecting Extremely Low pH in Saccharomyces cerevisiae

“…In addition, indole derivatives are often used as preferred structures in drug discovery and synthesis [40][41][42]. Although they show important biological activities, there are few reports on their optical properties due to the limitation of synthetic methods [43][44][45][46].…”

Maculatic Acids—Sex Attractant Pheromone Components of Bald‐Faced Hornets

“…Considering that the amount of analyte was insufficient to infer the olefin geometry by NMR analysis,w es elected af lexible synthetic route that would provide each of the four possible stereoisomers.A sd epicted in Figure 4, aH orner-Wadsworth-Emmons mono-olefination of 2,6-hexanedione [19] using tert-butyl-2-(dimethoxyphosphoryl)acetate afforded the esters 7 and 8 in 48 %combined yield, [20] which were separable by flash column chromatography using AgNO 3 -impregnated silica gel. With geometrically pure 7 and 8 in hand, as ubsequent Wittig reaction with the anion derived from (2-carboxyethyl)triphenylphosphonium bromide [21] provided am ixture of the E-and Z-alkenes 9 and 10.Aswe could not separate these dienes by flash chromatography (using silica gel or AgNO 3impregnated silica gel), they were purified by RP-HPLC and assigned the geometry of the D (2,3) and D (7,8) olefin functions in each isomer following analysis of NOESY spectra, as indicated in Figure 3.…”