Intramolecular cyclization of delta-iminoacetylenes: a new entry to pyrazino[1,2-a]indoles
Giorgio Abbiati1, Antonio Arcadi, Alessandra Bellinazzi
1Istituto di Chimica Organica Alessandro Marchesini, Facoltà di Farmacia, Università degli Studi di Milano Via Venezian 21, 20133 Milano, Italy. giorgio.abbiati@unimi.it
Abstract:
[reaction: see text] The synthesis of the pyrazino[1,2-a]indole nucleus was achieved by intramolecular cyclization of several 2-carbonyl-1-propargylindoles in the presence of ammonia. The reaction conditions were optimized using microwave heating and a pool of catalysts. Cyclization of 1-alkynylindole-2-carbaldehydes was easily accomplished under standard heating conditions, whereas microwave heating contributed to reduced reaction times and improved overall yields. Moreover, a fine-tuning of the microwave irradiation time made possible the selective synthesis of both pyrazino[1,2-a]indole isomers. TiCl4 proved the catalytic system of choice to achieve pyrazinoindoles in satisfactory yields starting from 1-alkynyl-2-acetylindoles and 1-alkynyl-2-benzoylindole derivatives. Also in these cases, microwave heating contributed to faster reactions and improved yields. The uncatalyzed versus catalyzed reaction mechanism is discussed.
More Related Videos
14:11Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
10:17Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Related Concept Videos
Aldehydes and Ketones with Amines: Imine and Enamine Formation Overview
Preparation of Diols and Pinacol Rearrangement
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization
Cycloaddition Reactions: Overview
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
