Fengzhi Zhang

Decarboxylative C—H Cross-Coupling of Azoles

An intermol. decarboxylative C-H cross-coupling between oxazoles and thiazoles with the rapid synthesis of functionalized polyazoles is described. E.g., in presence of Pd(OAc)2, copper carbonate, and 1,2-bis(dicyclohexylphosphino)ethane, decarboxylative C-H cross-coupling of thiazolecarboxylic acid I and oxazole II gave 80% bis(azole) III. [on SciFinder(R)]

Decarboxylative Cross-Coupling of Azoyl Carboxylic Acids with Aryl Halides

Decarboxylative cross-coupling of thiazole and oxazole-5-carboxylic acids with aryl halides is reported. Under a bimetallic system of catalytic palladium and a stoichiometric silver carbonate, a variety of (hetero)arylated azoles can be prepared in excellent yield.

Cu-Catalyzed Cascades to Carbocycles: Union of Diaryliodonium Salts with Alkenes or Alkynes Exploiting Remote Carbocations

Copper-catalyzed cascade reactions between alkenes or alkynes and diaryliodonium salts form carbocyclic products in a single step. Arylation of the unsaturated functional group is proposed to form a carbocation intermediate that facilitates hydride shift pathways to translocate the positive charge to a remote position and enables ring formation via a Friedel-Crafts-type reaction.

New approaches for the synthesis of erythrinan alkaloids.

A concise asymmetric total synthesis of (+)-erysotramidine is described, using chiral base desymmetrisation of a meso-imide, N-acyliminium addition, retro-Diels-Alder cycloaddition and radical cyclisation as the key steps. A related route, starting from a cyclobutene-fused imide, was explored, and established a novel construction of the Erythrina alkaloid skeleton using a key ring-opening/ring-closing metathesis step. Completion of this synthesis was thwarted by problems with the removal of an unwanted vinylic side-chain. Complementary enantiospecific routes to Erythrina systems were explored, starting from (L)-malic acid. Some unexpected observations were made concerning the diastereocontrol in malic acid-derived N-acyliminium ion cyclisations, where changing the protecting group of the alcohol function from acetate to OTIPS resulted in a dramatic change in diastereocontrol. Products from these reactions could be transformed into known intermediates for natural alkaloids, and into (+)-demethoxyerythratidinone itself, by means of radical cyclisations or intramolecular aldol reactions as the key steps.

An improved synthesis of 1,2-benzisoxazoles: TBAF mediated 1,3-dipolar cycloaddition of nitrile oxides and benzyne.

An efficient synthesis of a range of 1,2-benzisoxazoles using an improved 1,3-dipolar cycloaddition of nitrile oxides and benzyne is described. Key to the procedure is the in situ generation of the reactive nitrile oxide and benzyne reaction partners mediated by TBAF. Reactions are complete within 30 s, giving the target products in good to excellent yield.

An efficient entry to 1,2-benzisoxazoles via 1,3-dipolar cycloaddition of in situ generated nitrile oxides and benzyne

An efficient protocol for the synthesis of a range of 1,2-benzisoxazoles using an improved 1,3-dipolar cycloaddition of nitrile oxides and benzyne is described. Key to the procedure is the in situ generation of the reactive nitrile oxide and benzyne reactants simultaneously.

Fluoroquinolone derivatives and their anti-tubercular activities

Tuberculosis (TB) remains one of the most widespread and leading deadliest diseases, around one-third of the worlds population harbor a latent infection by Mycobacterium tuberculosis (MTB), and 5-10% eventually develop an active TB. The emergency of MTB new virulent forms as well as the co-infection between MTB and HIV alarming the serious problem in TB control and demanding the need for new drugs more potent than earlier with safe ADME profile. Fluoroquinolones are emerged as a large family of synthetic broad spectrum antibiotics, and some of them were recommended as the second-line agents for the treatment of TB mainly in cases involving resistance or intolerance to first-line anti-TB therapy by WHO. Numerous of FQs derivatives have been synthesized for seeking for new anti-TB agents, and some of them exhibited promising potency. This review aims to summarize the recent advances made towards the discovery of FQs derivatives as anti-TB agents and the structure-activity relationship of these derivatives.

Studies on novel macrocyclization methods of cembrane-type diterpenoids: a Stille cyclization approach to (±)-isocembrene

Abstract An efficient total synthesis of (±)-isocembrene via an intramolecular Stille cross-coupling reaction is described. A novel strategy towards the 1,3-diene-based cembrane-type macrocyclic diterpenoids has been realized.

Novel construction of the brassinolide side chain

Abstract A stereoselective synthesis of brassinolide, which involves construction of the side chain by a highly stereoselective aldol reaction between 20 S -6β-methoxy-3α,5- cyclo -5α-pregnane-20-carboxaldehyde 2 and ketone 3 or 4 catalyzed by l -proline, is described.

Copper-Catalyzed Selective Diphenylation of Carboxylic Acids with Cyclic Diaryliodonium Salts

Herein, we describe a novel one-step copper-catalyzed diphenylation of readily available aliphatic or (hetero)aromatic carboxylic acids with cyclic hypervalent diaryliodonium reagents. The selective diphenylation of benzoic acids with high atom economy can be achieved without observation of the arylation at the phenyl hydroxyl/thio/amino position. The valuable biphenyl esters with an additional iodo-substituent were obtained in good to excellent yields, which can be further transformed to diversified building blocks for the synthesis of bioactive natural products, pharmaceuticals, and functional materials. A wide range of different functional groups are compatible under the optimized reaction conditions.