Direct Catalytic Asymmetric Synthesis of β-Hydroxy Acids from Malonic Acid

Synthesis of Thioureas, Thioamides, and Aza-Heterocycles via Dimethyl-Sulfoxide-Promoted Oxidative Condensation of Sulfur, Malonic Acids, and Amines

Malonic acid and derivatives have been well-known to undergo monodecarboxylation under relatively mild conditions and have been exclusively used as a C2 synthon. We report herein their new application as a C1 synthon via double decarboxylation promoted by sulfur and dimethyl sulfoxide. In the presence of amines as nucleophiles, a wide range of thioureas and thioamides as well as N-heterocycles were obtained in good to excellent yields under mild heating conditions.

Microwave-Assisted Synthesis of 3-Hydroxy-2-oxindoles and Pilot Evaluation of Their Antiglaucomic Activity

Glaucoma is a widespread neurodegenerative disease for which increased intraocular pressure (IOP) is a primary modifiable risk factor. Recently, we have observed that compounds with oxindole scaffolds are involved in the regulation of intraocular pressure and therefore have potential antiglaucomic activity. In this article, we present an efficient method for obtaining novel 2-oxindole derivatives via microwave-assisted (MW) decarboxylative condensation of substituted isatins with malonic and cyanoacetic acids. Various 3-hydroxy-2-oxindoles were synthesized using MW activation for 5–10 min with high yields (up to 98%). The influence of novel compounds applied in instillations on IOP was studied in vivo on normotensive rabbits. The lead compound was found to reduce the IOP by 5.6 Torr (ΔIOP for the widely used antiglaucomatousic drug timolol 3.5 Torr and for melatonin 2.7 Torr).

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Asymmetric synthesis of δ-substituted-β-keto esters and β-substituted ketones via carboxyl-assisted site- and enantio-selective addition reactions

Highly site- and enantio-selective additions of polyfunctional nucleophiles to imines or carbonyls were achieved via a carboxyl-assisted strategy, affording δ-substituted-β-keto esters and β-substituted ketones with good yield and enantioselectivity.

Yb(OTf)3 catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles

A Yb(OTf)₃ catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles was achieved, affording a variety of multifunctional 3-ylideneoxindoles with good yields and Z/E selectivities (64%-89% yield, 78 : 22->99 : 1 Z/E). Importantly, an operationally simple, one-pot sequential catalytic synthesis of 3-ylideneoxindoles was also developed. Additionally, a cross [1,3]-rearrangement experiment and nonracemic transformation were also carried out, which indicated a concerted rearrangement mechanism of this methodology.

Switching of Enantioselectivity in the Cu-Catalyzed Asymmetric Decarboxylative Aldol Reaction of Tryptanthrin with β-Keto Acids: An Unexpected Counteranion Effect

Cu-bisoxazoline-catalyzed enantioselective decarboxylative aldol reaction of tryptanthrin with aryl-substituted β-keto acids is developed, providing a straightforward approach to deliver a series of phaitanthrin A analogues. Both enantiomers of the products can be obtained with good to high enantioselectivity in the presence of a single chiral ligand by simply changing the copper salts. Based on the X-ray crystallographic analysis of chiral Cu(II)-bisoxazoline complexes, the tentative stereochemical models are presented to account for the observed counteranion-induced switching in enantioselectivity.

Asymmetric Construction of α-Substituted β-Hydroxy Lactones via Ni Catalyzed Decarboxylative Addition Reaction

We described a Ni-bidentate oxazoline catalyzed highly enantio- and diastereoselective decarboxylative aldol reaction of 2-oxotetrahydrofuran-3-carboxylic acid/2-oxochromane-3-carboxylic acid derivatives with different kinds of carbonyls. Under optimal reaction conditions, α-substituted β-hydroxy butyrolactones and dihydrocoumarins with an all-carbon quaternary stereocenter have been generated with high levels of functional-group compatibility. Furthermore, proficient transformations of products were also described, in which an aliphatic tertiary alcohol and a multi-substituted 1,4-diol were smoothly constructed through hydrogenation and ring-opening reaction, respectively.

Stereoselective Copper-Catalyzed Direct Aldol Reaction of β, γ-Unsaturated α-Ketoesters with Coumaran-3-Ones

An efficient direct aldol reaction between coumaran-3-ones and β, γ-unsaturated α-ketoesters by virtue of a chiral copper complex is developed. A series of coumaran-3-one derivatives containing chiral tertiary alcohol structures are obtained in excellent yields and stereoselectivities.

Divergent Synthesis of Methylisatoid and Tryptanthrin Derivatives by Ph3P-I2-Mediated Reaction of Isatins with and without Alcohols

A novel phosphonium-mediated reaction of isatins is described. In the presence of alcohol, the reaction proceeds to furnish C-12 modified tryptanthrin derivatives. Without alcohol, self-dimerization of isatins gives rise to tryptanthrin and its analogs. This divergent and step-economic approach provides a facile access to diverse indoloquinazoline structures including the natural alkaloids, methylisatoid and cephalanthrin B, in high yields from simple precursors under mild and metal-free reaction conditions.

Synthesis of 6-substituted indoloquinazolinones from arynes and 2-acyl-4-quinazolinones: a transition-metal free C–N and C–C bond formation strategy

A versatile transition-metal free synthetic strategy has been developed for the direct synthesis of 6-substituted indoloquinazolinones from 2-acyl-4-quinazolinones and aryne precursors. This cascade strategy proceeds via successive C–N and C–C bond formation in a single reaction vessel.

Ni(II)-Catalyzed Enantioselective Synthesis of β-Hydroxy Esters with Carboxylate Assistance

A Ni-oxazoline complex-catalyzed asymmetric decarboxylative aldol reaction between malonic acid half-oxyesters and various carbonyls with carboxylate assistance was developed, affording structurally diverse β-hydroxy esters with good yields and enantioselectivities under mild conditions. Importantly, the broad substrate scope of this methodology enabled rapid accesses to several natural products and their analogues as exemplified by phenylpropanoid, phaitanthrin B, and phthalide.

Stereoselective construction of deoxy-cruciferane alkaloids by NHC-catalyzed intramolecular annulation of homoenolate with quinazolinone

Novel NHC-catalyzed intramolecular stereoselective [3 + 2] cycloaddition of enal with quinazolinone is developed to construct a pyrroloindoloquinazolinone scaffold of deoxy-cruciferane alkaloids.

Organocatalytic Decarboxylative Cyanomethylation of Difluoromethyl and Trifluoromethyl Ketones

An efficient organocatalytic method for the synthesis of difluoromethyl and trifluoromethyl substituted β-hydroxynitriles is introduced. The decarboxylative cyanomethylation of fluorinated ketones with readily available cyanoacetic acid gives a variety of tertiary alcohols in high yields and without concomitant water elimination. The reaction occurs in the presence of catalytic amounts of triethylamine, can be upscaled and applied to chlorofluoromethyl ketones and difluoromethyl ketimines.

Efficient chiral 1H NMR analysis of indoloquinazoline alkaloids phaitanthrin A, cephalanthrin-A and their analogues with a chiral phosphoric acid

A chiral phosphoric acid promoted enantioselective NMR recognition and determination of indoloquinazoline alkaloids phaitanthrin A, cephalanthrin-A and their analogues was described, which conveniently reveals their optical purities with high accuracy. Besides, pyrazine type tertiary alcohols, cyclic amino alcohols and diamines can also be well resolved under optimal conditions. Importantly, this methodology was further employed in the direct analysis of reaction mixtures of amino acid metal salt catalyzed asymmetric synthesis of phaitanthrin A, providing access to the optimized reaction conditions in high efficiency.

Catalytic enantioselective aldol reactions

Recent developments in catalytic asymmetric aldol reactions have been summarized.

Organocatalytic decarboxylative aldol reaction of β-ketoacids with α-ketophosphonates en route to the enantioselective synthesis of tertiary α-hydroxyphosphonates

γ-Aroyl tertiary α-hydroxyphosphonates with a chiral quaternary centre were synthesized via a facile organocatalyzed decarboxylative aldol reaction between β-ketoacids and α-ketophosphonates.