Chemoselective intramolecular annulation of 3-alkylindolines into dihydro or tetrahydrofuro[2,3-b]indoles

Abstract

3-Alkyl-2-hydroxyindolines, conveniently prepared from 2-hydroxyindolenines and a Grignard reagent, cyclize in the aprotic solvent tetrahydrofuran to afford tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles, while in the protic solvent methanol the chemoselectivity changed to give dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles. The steric effect of the alkyl group on the reactivity of 3-alkyl-2-hydroxyindolines is discussed for both processes. The ring transformation of tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles into dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles via γ-lactone imines is also discussed. Keywords: furo[2,3-b]indoles, α-cyano-γ-lactones, chemoselectivity, ring transformation, β-enamino esters.

Formation of Transient Intermediates in Low-Temperature Photosensitized Oxidation of an 8-13C-Guanosine Derivative

“…On the basis of these results, we propose the carbamic acid structures 6 and 7 for the two transient intermediates (Chart ). It has been reported that the chemical shifts of carbonyls in compounds with similar CNCOO structures are above 161 ppm − and the chemical shifts of carbonyls in compounds with NHCOO structures are ∼150 ppm − (Chart ), which correlate very well with our structure assignments. Compounds 6 and 7 readily decompose to form 5 and CO 2 .…”

Configuration, stereodynamics and crystal structure of 3-substituted-2-oxofuro[2,3-b]indoles

“…Melting points were determined on a Fisher-Johns apparatus and are uncorrected. IR spectra were obtained using a Perkin-Elmer 16F PC spectrophotometer, 1 H and 13 C NMR spectra on a Varian XL300GS spectrometer working at 300 and 75.4 MHz, respectively. All chemical shifts are reported in δ units relative to TMS.…”

Unimolecular rearrangements of ketene‐O,O‐acetals and fragmentations occurring in the gas phase

“…Column chromatography was performed on Silica Gel 60 (230–400 mesh) from Aldrich. Ketene acetals 1a, 1b, 2a and 2b and 2‐indolyl cyanomalonates 4a – e were synthesized as described8 from the corresponding methyl 3‐cyano‐3a‐alkyl‐2‐oxo‐2,3,3a,8a‐tetrahydro‐8 H ‐furo[2,3‐ b ]indole‐8‐carboxylates 8, 19, 20…”