Accessing substituted pyrrolidines via formal [3+2] cycloaddition of 1,3,5-triazinanes and donor-acceptor cyclopropanes

Lewis Acid-Enabled Chemodivergent Cycloadditions of Donor-Acceptor Cyclopropanes with Indoline-2-Thiones

Lewis acid-enabled reactions of donor-acceptor cyclopropanes (DACs) with indoline-2-thiones are reported. The reaction exhibits tunable annulation depending on the Lewis acid and the substituent at N1 of the indoline-2-thiones. With AlCl3 as the Lewis acid and 1-isopropylindoline-2-thiones as reactants, a direct ring opening with DACs, followed by intramolecular nucleophilic addition/dehydration takes place leading to the formation of dihydro-2H-thiepino[2,3-b]indoles in moderate to good yields. Using Yb(OTf)3 as promoter and 1-unsubstituted indoline-2-thiones as reactants, a (3 + 2) cycloaddition with DACs accompanied by sulfur rearrangement nucleophilic addition/dehydration takes place to give 3-indolyl-4,5-dihydrothiophenes in moderate yields. In addition, the synthetic transformation of 3-indolyl-4,5-dihydrothiophene to sulfone and indole-based axially chiral scaffolds further extends the synthetic utility and structural complexity.

Stereoretentive Catalytic [3 + 2]/[3 + 3]-Cycloaddition of Nonracemic Donor-Acceptor Cyclopropanes: Synthesis of Substituted Pyrrolidines and 1,2-Oxazinanes

A highly enantioselective preparation of substituted pyrrolidines and 1,2-oxazinanes has been achieved via stereoretentive [3 + 2]/[3 + 3]-cycloaddition of nonracemic donor-acceptor cyclopropanes with imines, triazines, and nitrones in good to high yields with broad scope under mild reaction conditions. In comparison with the well-documented approach to donor-acceptor cyclopropane reactions using racemic cyclopropane reactants and a catalyst with chiral ligands, this report features applications of enantioenriched donor-acceptor cyclopropanes as cycloadduct reactants with achiral catalysts.

Synthesis of Chromeno[2,3-d]pyrimidin-5-one Derivatives from 1,3,5-Triazinanes via Two Different Reaction Pathways

1,3,5-Triazinanes, as a kind of versatile building block, are applied in the synthesis of chromeno[2,3-d]pyrimidin-5-one derivatives via two different reaction modes, which perfectly exhibits the powerful function of 1,3,5-triazinane as a three-atom synthon along with the structure variation of another substrate. The two annulation reactions proceed under mild conditions and bear broad substrate scope and high yield.

Synthesis of α-Amino Tertiary Alkylperoxides by Lewis Acid-Catalyzed Peroxidation of 1,3,5-Triazines

α-Substituted peroxides have been found in natural products and are widely used as anti-malarial agents. Zn(OTf)₂ -catalyzed peroxidation of 1,3,5-triazines has been developed, accessing diversely substituted α-amino tertiary alkylperoxides with high efficiency. Mechanistic investigations and useful synthetic application of the products have also been presented.

Recent Advances of 1,3,5-Triazinanes in Aminomethylation and Cycloaddition Reactions

1,3,5-Trisubstituted 1,3,5-triazinanes (hexahydro-1,3,5-triazines), as stable and readily available surrogates for formaldimines, have found extensive applications for the construction of various nitrogen-containing compounds. The formaldimines, formed in situ from this reagent class, can participate in various aminomethylation and cycloaddition­ reactions. This short review presents recent advances in this field with emphasis on the conceptual ideas behind the developed methodologies and the reaction mechanisms.

1 Introduction

2 Aminomethylations with 1,3,5-Triazinanes

3 Cycloadditions with 1,3,5-Triazinanes

3.1 Use of 1,3,5-Triazinanes as Two-Atom Synthons

3.2 Use of 1,3,5-Triazinanes as Three-Atom Synthons

3.3 Use of 1,3,5-Triazinanes as Four-Atom Synthons

3.4 Use of 1,3,5-Triazinanes as Six-Atom Synthons

4 Conclusions

Stereocontrolled [3+2] Cycloaddition of Donor-Acceptor Cyclopropanes to Iminooxindoles: Access to Spiro[oxindole-3,2'-pyrrolidines]

A novel stereocontrolled assembly of spiro[oxindole-3,2'-pyrrolidines] via [3+2]-cycloaddition of donor-acceptor cyclopropanes to electron-poor ketimines, iminooxindoles, was developed. The method allows for efficient employment of common readily available donor-acceptor cyclopropanes, functionalized with ester, keto, nitro, cyano etc. groups, and N-unprotected iminooxindoles. The stereospecificity of the initial S_N2-like imine attack on a cyclopropane molecule together with a high diastereoselectivity of further C-C bond formation facilitate a rapid access to spiro[oxindole-3,2'-pyrrolidines] in their optically active forms. Preliminary in vitro testing of the synthesized compounds against LNCaP (p53+) and PC-3 (p53-) cells revealed good antiproliferative activities and p53-selectivity indices for several compounds that are intriguing in terms of their further investigation as inhibitors of MDM2-p53 interaction.

Rhodium(ii)-catalyzed annulation of N-sulfonyl-1,2,3-triazoles with 1,3,5-triazinanes to produce octahydro-1H-purine derivatives: a combined experimental and computational study

The Rh(ii)-catalyzed annulation of N-sulfonyl-1,2,3-triazoles with 1,3,5-triazinanes leading to the octahydro-1H-purine derivatives with moderate to good yields is described in this communication.

Donor–acceptor cyclopropanes as ortho-quinone methide equivalents in formal (4 + 2)-cycloaddition to alkenes

A new reactivity of donor–acceptor cyclopropanes as synthetic equivalents of o-quinone methides was revealed for 2-hydroxyarylcyclopropane diesters in their formal (4 + 2)-cycloaddition to alkenes yielding chromanes.