Stereocontrolled Solid-Phase Synthesis of a 90-Membered Library of Indoline-Alkaloid-like Polycycles from an Enantioenriched Aminoindoline Scaffold

Chiral Transient Directing Group Strategies in Asymmetric Synthesis

The development of novel methodologies for catalytic enantioselective functionalization reactions enabled by chiral transient directing groups is accompanying in a paradigm shift in the field of asymmetric synthesis. In particular, these highly atom- and step-economic enantioinduction processes commonly proceed either via enantioselective C-H functionalization, or via enantioselective hydroarylation of the pro-chiral substrates generating point, axial or planar chirality. The use of the transient directing group strategy in C-H functionalizations precludes the stoichiometric installations and removal of directing groups and enables efficient, more compatible and economical chemical routes. This minireview highlights asymmetric transition-metal-catalyzed methodologies involving chiral transient directing groups together with the scope, utility and future perspective of the field.

Kinetic Resolution of 2-Substituted Indolines by N-Sulfonylation using an Atropisomeric 4-DMAP-N-oxide Organocatalyst

The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6-19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.

Solvent-free, microwave-assisted N-arylation of indolines by using low palladium catalyst loadings

Indoline-based compounds are abundant in nature, and the indoline skeleton is an often-encountered scaffold in a range of biologically active alkaloids, pharmaceutically active compounds, and functional molecules (e.g., sensitizers for solar cells). The wide range of uses warrants further interest in the structural modification of this class of compounds. A series of substituted N-aryl indolines is prepared by a solvent-free, palladium-catalyzed procedure. The procedure requires only low loadings of catalyst, uses microwave irradiation, and starts from commercially available substrates. The method proceeds in good yields and in short reaction times with aryl bromides, chlorides, and iodides, also on 2-substituted indolines. The combination of solvent-free methods with microwave heating will further increase in importance in the search for more environmentally acceptable synthesis methods.

Efficient and General Synthesis of 3-Aminoindolines and 3-Aminoindoles via Copper-Catalyzed Three Component Coupling Reaction

An efficient three component coupling (TCC) reaction toward a variety of 3-aminoindoline and 3-aminoindole derivatives has been developed. This cascade transformation proceeds via the copper-catalyzed coupling reaction between 2-aminobenzaldehyde, secondary amine, and alkyne leading to propargylamine intermediate, which, under the reaction conditions, undergoes cyclization into the indoline core. The latter, upon treatment with a base, smoothly isomerizes into indole. Alternatively, indole can directly be synthesized in a one-pot sequential reaction.

Biology-Oriented Synthesis of Stereochemically Diverse Natural-Product-Derived Compound Collections by Iterative Allylations on a Solid Support

A strategy aiming at the introduction of stereocenters into polymer-bound natural-product-derived and -inspired compound collections is presented. Treatment of immobilized aldehydes with Brown's pinene-derived allylboranes results in the stereoselective formation of homoallylic alcohols with up to 89 % ee (ee=enantiomeric excess). Subsequent iterative ozonolysis-allylation sequences with up to three allylations on a solid support give access to 1,3-polyols with different relative configurations. Esterification with acryloyl chloride and final ring-closing metathesis yields alpha,beta-unsaturated delta-lactones with multiply oxygenated side chains, a substructure found in a group of natural products with a broad range of biological activity. The flexibility of the approach is exemplified by the parallel synthesis of all eight diastereomers of cryptocarya diacetate on a solid support. The individual isomers are obtained in overall yields of 40-60 % over 10 steps and with 63-85 % diastereoselectivity for the major isomer.

Catalytic enantioselective domino oxa-michael/aldol condensations: asymmetric synthesis of benzopyran derivatives

The first direct organocatalytic asymmetric domino oxa-Michael/aldol condensation reaction is presented. The unprecedentedly simple, chiral, pyrrolidine-catalyzed asymmetric domino reactions between salicylic aldehyde derivatives and alpha,beta-unsaturated aldehydes proceed with high chemo- and enantioselectivities to give the corresponding chromene-3-carbaldehyde derivatives in high yields and with ee values of 83-98%.