Synthesis and Functionalization of Thiophosphonium Salts: A Divergent Approach to Access Thioether, Thioester, and Dithioester Derivatives.

Herein, we report a straightforward practical method for efficiently obtaining a diverse range of thiophosphonium salts. This method involves the direct coupling of commercially available thiols and aldehydes with Ph3P and TfOH. The setup is simple and carried out in a metal-free manner. The synthetic utility of these salts is demonstrated through various examples of C-P bond functionalizations, enabling the synthesis of thioether, deuterated thioether, thioester, and dithioester derivatives. These products, which serve as valuable building blocks, are obtained in high yields.

Cascade Nucleophilic Addition-Cyclic Michael Addition of Arynes and Indoles Bearing Michael Acceptor: A Strategy to Construct Pyrroloacridines and Study of Their Physicochemical Properties.

A facile synthetic approach to 6H-pyrrolo[3,2,1-de]acridines has been developed by using cascade N-nucleophilic addition-cyclic Michael addition process of arynes and indoles substituted with Michael acceptors under metal-free conditions. Additionally, photophysical studies of a few of the newly synthesized pyrroloacridine compounds indicated good fluorescence emission properties.

A Method to Access Highly Functionalized Dibenzobicyclo[3.2.1]octadienones: Application to the Construction of the 6/6/5/6/6 Carbon Skeleton of Rubialatin A.

The dibenzobicyclo[3.2.1]octadienone scaffold, which has been found in naphthocyclinones, engelharquinones, rubialatin A, etc., has been synthesized under mild transition metal-free conditions by aryne insertion reaction with 2-keto-1,3-indandiones. The application of this methodology has been demonstrated for the synthesis of the 6/6/5/6/6 scaffold of rubialatin A. 1H NMR experimental studies confirm that the reaction proceeds through the formation of benzocyclobutane followed by a 7-member carbocycle ring.

Organocatalytic, Chemoselective Hydrophosphenylation/oxa-Michael Addition Cascade toward Diastereo- and Enantioenriched 1,3-Dihydroisobenzofuryl Phosphonates.

An efficient method for the construction of chiral C-P bond via an enantioselective 1,2-hydrophosphenylation followed by an oxa-Michael addition cascade of ortho-formyl chalcones has been developed. This provides the diastereoenriched ( cis)-1,3-dihydroisobenzofuryl phosphonates with excellent enantioselectivities (up to >99%). The origin of enantio- and diastereoselectivity is induced by using a chiral bifunctional organocatalyst. Further, functionalization to highly enantioselective 3-substituted phthalides has also been demonstrated.

Switchable Chemoselectivity for Organocatalytic, Asymmetric Malononitrile Addition to ortho-Formyl Chalcones.

Chemoselective 1,2- and 1,4-addition of malononitriles to ortho-formyl chalcones using cinchona alkaloid based bifunctional chiral organocatalysts has been shown by tuning the electronic nature of the malononitriles. Alkyl (hard) malononitriles undergo an asymmetric 1,2-addition followed by oxa-Michael reaction cascade to afford 1,3-disubstituted isobenzofurans with high enantio- and diastereoselectivity. Aryl (soft) malononitriles proceed through 1,4-addition followed by an aldol reaction cascade to provide indanols, having three consecutive stereocenters, in good yields and with good to excellent enantio- and diastereoselectivites.

Organocatalytic, enantioselective synthesis of benzoxaboroles via Wittig/oxa-Michael reaction Cascade of α-formyl boronic acids.

An unprecedented enantioselective synthesis of 3-substituted benzoxaboroles has been developed. An in situ generated ortho-boronic acid containing chalcone provides the chiral benzoxaboroles via an asymmetric oxa-Michael addition of hydroxyl group attached to the boronic acid triggered by the cinchona alkaloid based chiral amino-squaramide catalysts. In general, good yields with good to excellent enantioselectivities (up to 99%) were obtained. The resulting benzoxaboroles were converted to the corresponding chiral ß-hydroxy ketones without affecting the enantioselectivity.

Synthesis of polysubstituted quinolines via transition-metal-free oxidative cycloisomerization of o-cinnamylanilines.

An efficient synthesis of 2-aryl 4-substituted quinolines from stable and readily available o-cinnamylanilines, prepared from anilines and cinnamylalcohols, has been developed. The reaction occurred via a regioselective 6-endo-trig intramolecular oxidative cyclization using KO(t)Bu as a mediator and DMSO as an oxidant at rt. The reaction showed a broad substrate scope with good to excellent yields.