Microwave‐Assisted Solvent‐Free Synthesis of Hexahydrochromeno[4,3‐b]pyrroles

Abstract

Keywords: Cycloaddition / Microwave-assisted synthesis / Solvent-free synthesis / YlidesWe report the microwave-assisted solvent-free synthesis of hexahydrochromeno[4,3-b]pyrroles. Intramolecular 1,3-dipolar cycloadditions proceed under these conditions within 15 min in 80% yields. Moreover, we have observed pro- [a]

Microwave‐Assisted 1,3‐Dipolar Cycloaddition: an Eco‐Friendly Approach to Five‐Membered Heterocycles

“…Scheme 30. TiO 2 -impregnated silica gel was used as a solid-supported catalyst for the synthesis of dispiropyrrolo-isoquinoline ring systems in one-pot, three-component reactions as illustrated in Scheme 31. [71] Microwave-induced reactions between tetrahydroisoquinoline-3-carboxylic acid (91) and acenaphthenequinone (92) in the presence of 2-arylidene-1,3-indanediones 93 lead to single cycloadducts in high yields. Scheme 31. Solution-phase syntheses of proline-fused heterocyclic systems by the microwave-assisted intermolecular 1,3-dipolar cycloaddition approach have been reported.…”

“…[90] Microwave irradiation has also been used to promote the intramolecular cycloadditions of azomethine ylides resulting from condensations of O-allylic and O-propargylic salicylaldehydes with N-alkyl glycine esters. [91,92] Two selected examples leading to the syntheses of the tricyclic compounds 128 and 130 are shown in Scheme 43. [90] Parallel comparative reactions were carried out under conventional reaction conditions, leading to the conclusion that the microwave procedure favors the reaction times and the purities of the crude products, which are obtained in comparable yields.…”

“…With N-benzyl glycine ethyl ester as the azomethine ylide precursor, slightly more forcing conditions (300 W, 200°C for 15 min) were required. [92] On the other hand, bulkier N-substituents (e.g., N-isopropyl) were found to slow the rate of cycloaddition or to prevent it altogether (e.g. N-tert-butyl, N-adamantyl).…”

1,3-Dipolar Cycloaddition in the Preparation of New Fused Heterocyclic Compounds via Thermal Initiation

“…One frequently used method for preparing azomethine ylides applies an aldehyde and an amino-substituted ester. Such a method was used in our laboratory and, under microwave irradiation, led to hexahydrochromeno[4,3- b ]pyrroles [4,5,6] and hexahydropyrrolo[3,2- c ]quinolines [7]. The procedure is shown in Scheme 1.…”

Microwave-Assisted Synthesis of Substituted Hexahydro-pyrrolo[3,2-c]quinolines

“…During microwave irradiation the 2,450 MHz frequency is typically used and, since the individual oriented polar molecules present cannot match the resulting very fast changes in the electric field, this results in the transformation of part of the applied energy into heat, thus producing a temperature increase [7,8]. In the past we have investigated intramolecular microwaveassisted 1,3-dipolar cycloaddition reactions of in situ generated azomethine ylides leading to hexahydrochromeno- [4,3-b]pyrroles 3 [9,10]. A simple protocol was developed for these reactions, whereby the ylides were generated under microwave irradiation by the reaction of ortho-(3-alkenyl)oxybenzaldehydes 1 with secondary amines 2, prepared in turn by N-alkylation of alkyl aminoacetates.…”