Catalytic Asymmetric Synthesis of 3,3′‐Diaryloxindoles as Triarylmethanes with a Chiral All‐Carbon Quaternary Center: Phase‐Transfer‐Catalyzed SNAr Reaction

Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all‐carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the S_NAr reaction of 3‐aryloxindoles under phase‐transfer conditions. The presence of a urea moiety in the chiral phase‐transfer catalyst was important for obtaining high enantioselectivity in this reaction.     

A Cascade Synthesis of Hetero‐arylated Triarylmethanes Through a Double 5‐endo‐dig Cyclization Sequence

A sequential two‐step method for the synthesis of hetero‐arylated triarylmethanes through a Ag‐catalyzed sequential double cyclization–nucleophilic addition cascade is described. This methodology basically involves an initial 5‐endo‐dig cyclization of o‐alkynyl anilines to provide 2‐substituted indole derivatives, which then react with 2‐(2‐enynyl)‐pyridines to afford indolizine‐containing unsymmetrical triarylmethanes through another 5‐endo‐dig cyclization.     

Tandem regioselective synthesis of tetrazoles and related heterocycles using iodine

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.     

A convenient and efficient copper-catalyzed synthesis of unsymmetrical and symmetrical diaryl chalcogenides from arylboronic acids in ethanol at room temperature

A simple and convenient approach for the synthesis of unsymmetrical diaryl chalcogenides (Te, Se, and S) has been developed by copper-catalyzed cross-coupling reaction of organoboronic acid with diaryl dichalcogenide in ethanol using NaBH₄ in air or oxygen. The present methodology is highly practical for the synthesis of unsymmetrical diaryl tellurides with various functionalities such as –NO₂, –F, –Br, and –COOH that have been obtained in good to excellent yields. Methodology is also effective for the synthesis of unsymmetrical diaryl selenides and sulfides. Moreover, symmetrical diaryl selenides have also been obtained from arylboronic acids using elemental selenium powder under optimized reaction conditions. The use of NaBH₄ is the key for the development of milder reaction conditions, which enable the construction of unsymmetrical diaryl chalcogenides from boronic acid substrates in ethanol at room temperature.     

Novel synthesis of unsymmetrically substituted s-tetrazines

The synthesis of unsymmetrical 3-aryl and 3-heterocyclic s-tetrazines has been examined and the scope of the reaction and the product distribution is discussed. The products included unsymmetrical and symmetrical s-tetrazines, hydrazines, diimides, tetrazoles and triazoles with the composition of the mixtures with respect to structural type varying with the individual reactions. Some transformations with the system are discussed.     

Synthesis of novel dithiocarbamates and xanthates using dialkyl azodicarboxylates: SN bond formation

A one?pot three?component route for the synthesis of a novel category of dithiocarbamates or xanthates is developed by a reaction of in-situ generated dithiocarbamic acids or xanthates with dialkyl azodicarboxylates under mild and catalyst-free conditions. The reaction is characterized by a wide scope, high efficiency and straightforward isolation protocol. The synthetic utility of the dithiocarbamates and xanthates was demonstrated on the preparation of symmetrical and unsymmetrical thioureas, isothiocyanates, and thiocarbamates.     

Cationic Pd(II)/bipyridine-catalyzed addition of arylboronic acids to arylaldehydes. One-pot synthesis of unsymmetrical triarylmethanes

Cationic Pd(II) complex-catalyzed addition of arylboronic acids to aldehydes with low catalyst loading was developed with high yields. One-pot synthesis of unsymmetrical triarylmethanes from arylboronic acids, aryl aldehydes, and electron-rich arenes was achieved in high yields.     

Scalable synthesis of enantiomerically pure bicyclo[2.2.2]octadiene ligands

An operationally simple and scalable synthesis of enantiomerically pure bicyclo[2.2.2]octadiene (bod*) ligands relying on an organocatalytic one-pot Michael addition-aldol reaction with cheap 2-cyclohexenone and phenylacetaldehyde is presented. The crystalline bicyclic product 4a (6-hydroxy-5-phenylbicyclo[2.2.2]octan-2-one) is transformed into phenylbicyclo[2.2.2]oct-5-en-2-one 2, a versatile starting material for the 2-step synthesis of both symmetrical, such as Hayashi's Ph-bod* ligand, as well as novel unsymmetrical chiral dienes.     

Synthesis of cyclic disulfides using didecyldimethylammonium bromide as phase transfer catalyst

A convenient, practical and general method for the synthesis of symmetrical and unsymmetrical cyclic disulfides based on the reaction of sulfur with sodium sulfide in the presence of didecyldimethylammonium bromide (DDAB) as a phase transfer catalyst is described.     

Practical synthesis of unsymmetrical ureas from isopropenyl carbamates

A very convenient method for the synthesis of unsymmetrical ureas is described, based on isopropenyl carbamates. The synthetic efficiency of traditional methods for urea formation, such as use of phosgene or alkyl and aryl carbamates, is limited by the formation of symmetrical urea side products or reaction reversibility. Isopropenyl carbamates react with amines cleanly and irreversibly and give unsymmetrical ureas in high yield and purity. This method is ideal for the rapid synthesis of compound libraries.     

One-Pot Synthesis of Symmetrical and Unsymmetrical Diarylmethanes via Diborylmethane

A one-pot synthesis of diarylmethanes from air-stable diborylmethane via the Suzuki-Miyaura cross-coupling reaction is described. The present approach realizes the synthesis of various symmetrical and unsymmetrical diarylmethanes in good to excellent yields.     

Organocatalyzed synthesis of ureas from amines and ethylene carbonate

A new solventless method for the synthesis of symmetrical and unsymmetrical ureas, starting from ethylene carbonate and amines, is reported. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene(TBD) and thioureas have been found to be efficient organocatalysts for this reaction.     

Synthesis of new cholesterol- and sugar-anchored squaraine dyes: further evidence of how electronic factors influence dye formation

[reaction: see text] Synthesis of new quinaldine-based squaraine dyes linked to cellular recognition elements that exhibit near-infrared absorption (>740 nm) are described. Both product analysis and theoretical calculations substantiate the interesting electronic effects of various substituents in the dye formation reaction. These results are useful in the synthesis of symmetrical and unsymmetrical squaraine dyes that can have potential biological and photodynamic therapeutical applications.     

HMPA‐Promoted Siladifluoromethylation of Di‐, and Triarylmethanes with the Ruppert–Prakash Reagent

A mild and efficientmethod for the synthesis of α‐siladifluoromethylated di‐, and triarylmethanes via the reaction of di‐, and triarylmethanes with Ruppert–Prakash reagents, using LDA and HMPA at room temperature, was developed.     

Copper(II) Bromide–Catalyzed C-C/C-N Bond-Forming Reactions: Synthesis of Pyrrole-Incorporated Triarylmethanes

We have achieved a facile copper(II) bromide–catalyzed synthesis of 2,3,4-trisubtitued pyrrole incorporated into unsymmetrical triarylmethanes through direct replacement of hydroxyl group in the pyrrolyl phenyl methanol with electron-rich aromatic and heteroaromatic compounds. The newly developed method has been applied to a facile synthesis of a C2 symmetric bis-triarylmethane in which the two triarylmethanes were bridged through piperzine. The copper(II) bromide catalysis led to C-C bond formation at the C(5) position when the reacting partner was imidazole. In contrast, C-N bond formation took place with benzimdazole or 2-methylbenzimidazole.     

Inexpensive, one-pot synthesis of unsymmetrical disulfides using 1-chlorobenzotriazole

A new synthesis of unsymmetrical disulfides is described. The reaction of a thiol R1SH with 1-chlorobenzotriazole (BtCl) at -78 degrees C in DCM affords a high-yielding conversion to R1SBt without appreciable formation of the symmetrical disulfide R1SSR1. R1SBt is then reacted with R2SH to form the unsymmetrical disulfide in a one-pot sequence with green character that avoids the use of toxic and harsh oxidizing agents. The methodology has been developed for synthesis of various types of disulfides.     

Tris(pentafluorophenyl)borane [B(C6F5)3]-catalyzed Friedel-Crafts reactions of activated arenes and heteroarenes with α-amidosulfones: the synthesis of unsymmetrical triarylmethanes

Tris(pentafluorophenyl)borane [B(C₆F₅)₃] has found to be an efficient catalyst for Friedel-Crafts reactions between activated arenes or heteroarenes and α-amidosulfones. The products undergo further Friedel-Crafts reactions with activated heteroarenes leading to the synthesis of unsymmetrical triarylmethanes. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, highly regioselective, high yield, and broad applicability to various substrates.     

Synthesis of silylallene glycosides and diene diglycosides by C-glycosidation of D-glucal with 1,4-bis(trimethylsilyl)-2-butyne

[reaction: see text] Silylmethylallenyl glycosides, symmetrical and unsymmetrical diene glycosides, were synthesized by C-glycosidation with 1,4-bis(trimethylsilyl)-2-butyne in good yield. The nature of the product is controlled by the choice of Lewis acid, BF(3).OEt(2), or SnCl(4). The efficient construction of unsymmetrical diene glycosides was achieved in one pot on the basis of the order of addition of sugar starting materials.     

A facile and efficient Bi(III) catalyzed synthesis of 1,1-dihydroperoxides and 1,2,4,5-tetraoxanes

Bismuth triflate is a remarkably efficient and mild catalyst for the synthesis of both 1,1-dihydroperoxides and 1,2,4,5-tetraoxanes. The successful application of this methodology for the synthesis of both symmetrical and unsymmetrical tetraoxanes is demonstrated.     

A green synthesis of unsymmetrical triarylmethanes via indium (III) triflate catalyzed Friedel Crafts alkylation of o-hydroxy bisbenzylic alcohols under solvent free conditions

Using indium (III) triflate as a mild Lewis acid catalyst, the Friedel Crafts alkylation of o-hydroxy bisbenzylic alcohols with aromatic/heteroaromatic arenes under solvent free conditions was achieved to give the corresponding unsymmetrical triarylmethanes in high yields (up to 80% yield). Calculation of the different green metrics for the above reaction revealed it to have high atom economy (94–96%), high reaction mass efficiency (66–77%) and high carbon efficiency (70–80%). The Lewis acid was found to be air and moisture tolerant. The protocol was found to be operationally simple and can be carried out in an “open-flask” leaving behind water as the sole by product. Gratifyingly the Lewis acid catalyst could be recycled and reused up to 5 catalytic cycles without compromising much on the yield thus further highlighting the importance of the protocol.