Synthesis of Pyrrole and Carbazole Alkaloids

Abstract

An overview of recent transition metal-catalyzed syntheses of pyrroles and carbazoles is presented. The focus is on methods which have been applied to the preparation of biologically active naturally occurring pyrrole and carbazole alkaloids. For pyrroles, special attention is paid to silver(I)-catalyzed cyclization reactions. For carbazoles, iron(0)-mediated and palladium(0/II)-catalyzed cyclization reactions are highlighted and their broad range of applications is discussed.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

“…79 The total synthesis of rac-actinophyllic acid (173) was accomplished, which featured the one-pot construction of tetracyclic intermediate 174 through the cascade reaction of a carbocation generated from the TMSOTf-mediated ionization of indole with p-nucleophile enamido diene, followed by a spontaneous intramolecular cyclization of N-acyliminium ion (Scheme 48). Scheme 42 Reagents and conditions: (i) PEPPSI-IPr, t-BuONa, toluene, reflux; (ii) Pd 2 dba 3 , P(2-furyl) 3 , Bu 3 SnOMe, toluene, 100 C; (iii) NaHMDS, DMF, À40 C to rt; (iv) MeI, À40 C to rt; (v) LiAlH 4 , Et 2 O, rt; (vi) Dess-Martin, NaHCO 3 , CH 2 Cl 2 , rt.…”

“…Deprotection of the Boc group of 48 provided the known intermediate 49 for 43. Transformation of 48 to 42 was realized using the one-pot installation of the C13 hydroxy group via an allylic selenoxide [2,3]sigmatropic rearrangement (Scheme 4). 28 The rst synthesis of lecanindole D (50) was accomplished (Scheme 5).…”

Synthesis of 2,3,4,5-tetrasubstituted pyrroles and 1,4-dihydro-tetraarylpyrazines using acidic alumina as a heterogeneous catalyst

“…In addition, pyrroles have also been synthesized by the Huisgen reaction [20][21][22], cyclization of N-propargylic derivatives [23,24], including propargyl aziridines [25,26], through the cyclocondensation of vinyl azides with 1,3-dicarbonyls [27,28], transition-metal-catalyzed cyclization [29], [3 + 2] cycloadditions [30], and multi-component reactions [4,[31][32][33][34][35][36][37][38][39], among various other alternatives. Nevertheless, some of these methods need multiple steps, expensive or prefunctionalized substrates, and using reagents which generate halide wastes.…”

Total Syntheses of Carbazole Alkaloids Lansine F and Clauemarazole D

“…Carbazole alkaloids are widely presentedi nt he genus Clausena (Rutaceae) and exhibit ab road range of frameworks. [1] For example,l ansine F 1 [2] (Figure 1), isolated from Clausena rhizome, belongs to the pyrido [4,3-b]carbozole alkaloid family and has been found to inhibit the growth of several tumorc ell lines, while clauemarazoleD2, [3] isolated from the stems of Clausena emarginata,d isplays ac haracteristic cyclopenta[b]carbazole skeleton. To date, there is no literature precedent concerning the synthesis of lansine Fa nd clauemarazole D. Recently,w e developedavaluable approach for thed ivergent synthesis of carbazole alkaloids.…”