N-Indolyltriethylborate: A Useful Reagent for Synthesis of C3-Quaternary Indolenines

Abstract

N-Indolyltriethylborate was found to be a useful reagent for dearomatizing C3-alkylation of 3-substituted indoles with both activated and nonactivated alkyl halides to give C3-quaternary indolenines, pyrroloindolines, furoindoline, and hexahydropyridoindoline under mild reaction conditions. The utility of these reagents was demonstrated in the syntheses of a pyrroloindoline-4-cholestene hybrid and debromoflustramine B.

X‐Ray Characterization of an Electron Donor–Acceptor Complex that Drives the Photochemical Alkylation of Indoles

“…Gratifyingly, complete regioselectivity was achieved, with the C3-alkylated adducts being exclusively produced. Notably, while few metal-mediated protocols exist for the C3benzylation of 2,3-disubstituted 1H-indoles, [22] this chemistry offers the first methodology for the direct construction of indolenines adorned with a phenacyl moiety at C3 (4 b,c and 4 e). Of particular interest are the substrates with a pendant nucleophile, which cyclize onto the imine of 4 under the reaction conditions (Figure 3 e).…”

Mimicking the Main Events of the Biosynthesis of Drimentines: Synthesis of Δ8′‐Isodrimentine A and Related Compounds

“…For this purpose, after the sequential exposure of 4 to potassium tert ‐butoxide and triethylborane (allowing the formation of an indolyltriethylborate species), farnesyl bromide ( 8 ) served as the electrophile (Scheme ) . Under these conditions, complexation of the indole anion is supposed to enhance the C‐3 nucleophilicity by electron enrichment, therefore allowing the C‐3 quaternization.…”

“…For this purpose, after the sequential exposure of 4 to potassium tert-butoxide and triethylborane (allowing the formation of an indolyltriethylborate species), farnesyl bromide (8) [10] served as the electrophile (Scheme 2). [11][12][13] Under these conditions, complexation of the indole anion is supposed to enhance the C-3 nucleophilicity by electron enrichment, therefore allowing the C-3 quaternization. The direct trapping of the transitory indolenine by the appended diketopiperazine moiety allowed the formation of the tetracyclic ring system of drimentines just as in the biosynthetic proposal.…”

Iridium‐Catalyzed Enantioselective Intermolecular Indole C2‐Allylation

“…[9c-g] Intramolecular reactions can overcome the regioselectivity issues associated with intermolecular indole reactivity. [11] Several asymmetric indole C2-allylation procedures have been developed following this approach. [12] However,t hese strategies almost always lead to the formation of annulated C2-allylated indoles.Asearch of the literature revealed that the sole exception to this generalization comes from Tambar et al [13] who developed an innovative intramolecular route to branched, highly enantioenriched C2-allylated 3-amino indoles employing an enantioselective aza-Claisen rearrangement (Scheme 1, c).…”