g-yi Chen

A Novel, Highly Enantioselective Ketone Alkynylation Reaction Mediated by Chiral Zinc Aminoalkoxides

Kilogram-scale synthesis of the HIV reverse transcriptase inhibitor efavirenz was achieved by means of a highly enantioselective alkynylation of prochiral ketones 1 with alkynyllithium or alkynylmagnesium reagents in the presence of chiral zinc aminoalkoxides as mediators. With the achiral auxiliary 2,2,2-trifluoroethanol (R3 =CF3 CH2 ), the efavirenz precursor 2 (R1 =H, R2 =cyclopropyl) was obtained with an ee of 99.2%.

Synthesis of the 5-HT1D receptor agonist MK-0462 via a Pd-catalyzed coupling reaction

Abstract Application of a palladium-catalyzed coupling between 3 and 5a to the synthesis of the novel 5-HT 1D receptor agonist MK-0462 ( 1 ), a potential anti-migraine drug, is described.

Cyclopropylboronic acid: synthesis and Suzuki cross-coupling reactions

An efficient synthesis of cyclopropylboronic acid is reported. This compound undergoes efficient Suzuki-type coupling reactions with a range of aryl and heteroarybromides.

A simple, modular method for the synthesis of 3,4,5-trisubstituted pyrazoles.

A modular approach for the regiocontrolled preparation of pyrazoles bearing substituents on all three carbon atoms is described. Central to this method is the use of a switchable metal-directing group (MDG) to enable sequential direct lithiation of the 3- and 5-positions of the pyrazole ring. Pyrazole boronic esters obtained from these lithiated intermediates can undergo efficient Suzuki cross-coupling under the developed nonaqueous conditions, which minimize undesirable protolytic deboronation. Halogenation of the 4-position provides the means for substitution at the remaining carbon atom.

Enantioselective Pd-Catalyzed α-Arylation of N-Boc-Pyrrolidine: The Key to an Efficient and Practical Synthesis of a Glucokinase Activator

A short and practical synthesis of glucokinase activator 1 was achieved utilizing a convergent strategy involving S(N)Ar coupling of activated aryl fluoride 11 with hydroxypyridine 9. The key to the success of the synthesis was the development of a novel method for enantioselective formation of alpha-arylpyrrolidines during the course of the project. In this method, (-)-sparteine-mediated enantioselective lithiation of N-Boc-pyrrolidine was followed by in situ transmetalation to zinc and Pd-catalyzed coupling with aryl bromide 3, proceeding in 92% ee. This transformation allowed the preparation of compound 1 in a 31% overall yield over six steps.

Expanding the [1,2]‐Aryl Migration to the Synthesis of Substituted Indoles

The indole scaffold is a prevalent substructure of many natural products and biologically active compounds. The need for efficient and practical syntheses of indoles bearing a variety of substitution patterns provides a continual challenge to organic chemists. Despite the many diverse and creative approaches that have been used to assemble the indole nucleus, a general synthesis of indoles with control over the regioselective introduction of substituents at C2 and C3, is of tantamount importance. Herein we report a synthesis of substituted indoles 2 from readily accessible chloroacetophenones 1, which contain a 1-(2-aminophenyl)-2-chloroethanone core structure, and commercially available organometallic reagents [RM, Eq. (1)]. Of particular significance is the

Eine neue, hochenantioselektive Alkinylierung von Ketonen, die durch chirale Zinkaminoalkoxide gesteuert wird

Im Kilogramm-Masstab gelang die Synthese von Efavirenz, einem zugelassenen Hemmstoff der Reversen Transkriptase des HI-Virus. Dabei wurde die hochenantioselektive Alkinylierung der prochiralen Ketone 1 mit Alkinyllithium- oder Alkinylmagnesiumreagentien durch chirale Zinkaminoalkoxide unterstutzt. Mit 2,2,2-Trifluorethanol als achiralem Hilfsstoff (R3 = CF3CH2) wurde die Efavirenz-Vorstufe 2 (R1 = H, R2 = Cyclopropyl) in 99.2 % ee erhalten.

A divergent and selective synthesis of isomeric benzoxazoles from a single N-Cl imine.

A divergent and regioselective synthesis of either 3-substituted benzisoxazoles or 2-substituted benzoxazoles from readily accessible ortho-hydroxyaryl N-H ketimines is described. The reaction proceeds in two distinct pathways through a common N-Cl imine intermediate: (a) N-O bond formation to form benzisoxazole under anhydrous conditions and (b) NaOCl mediated Beckmann-type rearrangement to form benzoxazole, respectively. The reaction path also depends on the electronic nature of the aromatic ring, with the electron-rich aromatic rings favoring the rearrangement and the electron-deficient rings favoring the N-O bond formation. A Beckmann-type rearrangement mechanism via net [1,2]-aryl migration for the formation of 2-substituted benzoxazole is proposed.

A Practical Enantioselective Synthesis of Odanacatib, a Potent Cathepsin K Inhibitor, via Triflate Displacement of an α-Trifluoromethylbenzyl Triflate

An enantioselective synthesis of the Cathepsin K inhibitor odanacatib (MK-0822) 1 is described. The key step involves the novel stereospecific S(N)2 triflate displacement of a chiral alpha-trifluoromethylbenzyl triflate 9a with (S)-gamma-fluoroleucine ethyl ester 3 to generate the required alpha-trifluoromethylbenzyl amino stereocenter. The triflate displacement is achieved in high yield (95%) and minimal loss of stereochemistry. The overall synthesis of 1 is completed in 6 steps in 61% overall yield.

Enantioselective synthesis of an HCV NS5a antagonist.

A concise, enantioselective synthesis of the HCV NS5a inhibitor MK-8742 (1) is reported. The features of the synthesis include a highly enantioselective transfer hydrogenation of an NH imine and a dynamic diastereoselective transformation. The synthesis of this complex target requires simple starting materials and nine linear steps for completion.