ß-Strand inspired bifacial π-conjugated polymers.

Access to diverse, relatively high molecular weight soluble linear polymers without pendant solubilizing chains is the key to solution state synthesis of structurally diverse nanoribbons of conjugated materials. However, realizing soluble 1D-π-conjugated polymers without pendant solubilizing chains is a daunting task. Herein, inspired from the polypeptide ß-strand architecture, we have designed and developed novel bifacial π-conjugated polymers (M n: ca. 24 kDa) that are soluble (ca. 70 to >250 mM) despite the absence of pendant solubilizing chains. The impact of varying the bifacial monomer height on polymer solubility, optical properties, and interactions with small molecules is reported.

An expeditious route to the synthesis of the enantioenriched tetracyclic core of ergot alkaloids via an organocatalytic aldol reaction.

The synthesis of the tetracyclic skeleton of ergot alkaloids has been developed via a key organocatalytic enantioselective aldol reaction using paraformaldehyde as the C1-unit in the presence of thiourea catalyst followed by a key Pd-catalyzed directed coupling accelerated by the DavePhos ligand. Utilizing the aforementioned strategy, we have synthesized a key tetracyclic intermediate in up to 95% ee with high yield.

Catalytic asymmetric formal total syntheses of (+)- and (-)-cycloclavine.

We report an expeditious catalytic asymmetric approach to clavine alkaloids via a key Heck cyclization. This reaction sets the formation of vicinal stereocenters with excellent diastereoselectivity. Utilizing the aforementioned strategy, the formal total synthesis of cycloclavine (1) has been achieved via another key late-stage ester-aminolysis of 6.

Biomimetic Total Syntheses of Clavine Alkaloids.

Biomimetic total syntheses of either enantiomers of a number of ergot alkaloids, chanoclavine I (1b), chanoclavine I aldehyde (1c), pyroclavine (1e), festuclavine (1f), pibocin A (1g), 9-deacetoxyfumigaclavine C (1h), and fumigaclavine G (1i), have been achieved from seco-agroclavine (1a). The advanced intermediate for seco-agroclavine (1a) was synthesized via a key thiourea-catalyzed intramolecular nitronate addition onto α,ß-unsaturated ester.

Transition-Metal Free Oxidative Alkynylation of 2-Oxindoles with Ethynylbenziodoxolone (EBX) Reagents.

We report an efficient direct alkynylations of 3-alkyl/aryl 2-oxindoles employing ethynyl-1,2-benziodoxol-3(1H)-one (EBX) to afford a wide variety of 3-alkynyl-3-alkyl/aryl 2-oxindole under transition-metal free condition. In addition to activated carbonyl compounds viz. 2-oxindole-3-alkylcarboxylates, this direct alkynylations protocol works efficiently on 3-alkyl/aryl 2-oxindols as well thereby widening the scope even further. Eventually, a Pd(0)-catalyzed asymmetric decarboxylative allylation of few products is shown to furnish synthetically viable enantioenriched 2-oxindoles with C-3 quaternary stereocenters.

Total Syntheses of Pyroclavine, Festuclavine, Lysergol, and Isolysergol via a Catalytic Asymmetric Nitro-Michael Reaction.

A catalytic enantioselective construction of vicinal stereocenters is reported. The reaction takes advantage of thiourea-catalyzed intramolecular nitronate addition onto α,ß-unsaturated ester to afford exceptional levels of enantioselectivity (up to 97 % ee) with moderate diastereoselectivity (up to 4:1). Using this method, a cross-conjugated ester was synthesized in few steps, from which a 6-endo-trig cyclisation led to the formation of all required functionalities for total syntheses of ergot alkaloids. The strategy not only offers first total syntheses of ergot alkaloids, festuclavine (1 c), and pyroclavine (1 e), and but also an efficient and general approach to other congeners such as, lysergol (1 b), and isolysergol (1 d).

Catalytic Enantioselective Decarboxylative Allylations of a Mixture of Allyl Carbonates and Allyl Esters: Total Synthesis of (-)- and (+)-Folicanthine.

A highly enantioselective decarboxylative allylation of a mixture of enol carbonates and allyl esters has been achieved. The strategic viability of this methodology has been demonstrated through the total synthesis of cyclotryptamine alkaloids (-)- and (+)-folicanthine (1 a) and the formal total synthesis of (-)-chimonanthine (1 b), (+)-calycanthine (1 c), and (-)-ditryptophenaline (1 d).

Oxidative dimerization of 2-oxindoles promoted by KO(t)Bu-I2: total synthesis of (±)-folicanthine.

A 'transition-metal-free' oxidative coupling of 2-oxindoles has been demonstrated in the presence of 1.2 equiv each of potassium tert-butoxide and iodine. The method yields a diverse range of structurally different homo- and heterodimerized 2-oxindoles bearing vicinal all-carbon quaternary centers of great synthetic importance. A radical-driven pathway has been tentatively proposed.