Poly(1,2,4-oxadiazolidin-5-one)s synthesized by polycycloaddition of bisoxaziridines and diisocyanate

Tautomeric-Dependent Lactam Cycloaddition with Nitrile Oxide: Facile Synthesis of 1,2,4-Oxadiazole[4,5-a]indolone Derivatives

A concise, metal-free, and gram-scale strategy to convert indoline-2,3-diones to 1,2,4-oxadiazole[4,5-a]indolones through an improved [3 + 2] cycloaddition of α-ketone-lactam with nitrile oxides has been developed. The lactim form of the resonance structure of isatin in protic solvents is the key active dipolarophile that shows chemo- and regioselectivity under experimental and theoretical conditions. This strategy conveniently enabled the assembly of several 1,2,4-oxadiazole[4,5-a]indolines with a broad range of functional groups. Compounds 3a and 4b exhibit cytotoxicity in the NCI/ADR-RES, SKOV3, and OVCAR8 cell lines.

Enantioselective Vinylogous Organocascade Reactions

Cascade reactions are powerful tools for rapidly assembling complex molecular architectures from readily available starting materials in a single synthetic operation. Their marriage with asymmetric organocatalysis has led to the development of novel techniques, which are now recognized as reliable strategies for the one-pot enantioselective synthesis of stereochemically dense molecules. In recent years, even more complex synthetic challenges have been addressed by applying the principle of vinylogy to the realm of organocascade catalysis. The key to the success of vinylogous organocascade reactions is the unique ability of the chiral organocatalyst to transfer reactivity to a distal position without losing control on the stereo-determining events. This approach has greatly expanded the synthetic horizons of the field by providing the possibility of forging multiple stereocenters in remote positions from the catalyst's point of action with high selectivity, while simultaneously constructing multiple new bonds. This article critically describes the developments achieved in the field of enantioselective vinylogous organocascade reactions, charting the ideas, the conceptual advances, and the milestone reactions that have been essential for reaching highly practical levels of synthetic efficiency.

Macrocyclic and polymeric oxaziridine-derivatives

Macrocyclic and polymeric imines 5,5' and 6,6' are obtained in excellent yields by template-free polycondensation of 1,6-bis(4-formylbenzoyloxy)hexane (1) with commercially available 4,4'-methylene-bis(cyclohexylamine) (2) and with bis(2-amino-2-methylprop-1-yl)adipate dihydrochloride (4), respectively. The degree of macrocyclization during imine synthesis strongly depends on the diamine. Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry analysis and gel permeation chromatography (GPC) measurements show that (2) leads to more macrocyclic adducts than (4). The subsequent meta-chloroperoxybenzoic acid oxidation of polyimines 5,5' and 6,6' ($ \bar M_{\rm n} $ = 1650-11 200 g mol(-1) , $ \bar M_{\rm w} $ = 3800-27 350 g mol(-1) ) yields the corresponding polyoxaziridines 7,7' and 8,8' consisting of macrocyclic and linear polymeric structures ($ \bar M_{\rm n} $ = 1750-8050 g mol(-1) , $ \bar M_{\rm w} $ = 3250-15 800 g mol(-1) ). The synthesized polyoxaziridines are relatively stable and storable at room temperature.