Highly Diastereoselective TandemN-Alkylation-Mannich Reaction of α-Imino Esters

Umpolung Chemo- and Regioselective Cascade Addition of Diethylzinc to α-Diketones Followed by Intramolecular Michael Reaction: Stereoselective Synthesis of Highly Substituted 1- Indanones

Herein we report an efficient stereoselective umpolung 1,2-addition of Et₂Zn onto α-diketones followed by intramolecular cascade Michael cyclization. This strategy effectively delivers a broad range of substituted 1-indanones in excellent yields in a chemo- and regioselective fashion. Additionally, we performed a variety of synthetic transformations on the 1-indanone products. Furthermore, a hitherto-unexplored asymmetric variant of this methodology that provides up to 94:6 er using an easily accessible cinchona alkaloid ligand has been addressed.

Highly Selective Synthesis of α-Aminoamide Utilizing an Umpolung Reaction and Characteristics of α-Hydrazonoester

An umpolung reaction with α-hydrazonoesters was investigated, and it was found that α-N,N-dialkylaminoamides could be directly synthesized in yields up to 92% via a concomitant rearrangement of dialkylamino groups. As an application, a short synthesis of an inhibitor of glycine type-1-transporter was accomplished via subsequent functional group transformations in 28% overall yield.

N-Alkylation/aldol reaction of α-aldimino thioesters: a facile three-component coupling reaction

Theoretical calculation of the reactivity of α-imino thioesters indicates that they are very reactive substrates for Umpolung N-alkylation. In fact, treatment of α-aldimino thioesters with dialkylzinc reagents in the presence of aldehydes or imines gives three-component coupling products in good yields.

Synthesis of Tetramic Acid Derivatives via a Tandem Umpolung Alkylation/Reduction/Cyclization Reaction of γ-Hydrazono β-Ketoester

An efficient method for the one-pot synthesis of tetramic acid derivatives was developed utilizing tandem umpolung N-alkylation/reduction/cyclization of γ-hydrazono β-ketoester. By using this reaction as a key step, the total synthesis of the 3-spiro 7-hydroxamic acid tetralin which possesses an HDAC inhibitory activity was also achieved.

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

Unprecedented α-imino N-acyl pyrazoles were efficiently and selectively prepared through the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed reaction of nitrosoarenes with N-acyl pyrazoles via an N-nitroso aldol reaction/dehydration sequence. The α-imino acyl pyrazoles were demonstrated to be new versatile intermediates for practical one-pot syntheses of α-imino amides, dipeptide precursors, esters, and β-amino alcohols. The synthetic method competes with known protocols in terms of ready availability of the reagents and catalyst, mild and catalytic reaction conditions, gram-scale applicability, and scope of the α-imino acid derivatives achievable.

Tandem N, N-Dialkylation Reaction of N-Trimethylsilyl α-Iminoesters Utilizing an Umpolung Reaction and Characteristics of the Silyl Substituent: Synthesis of Pyrrolidine, Piperidine, and Iminodiacetate

Umpolung reactions of N-trimethylsilyl α-iminoester with organometallics gave directly N-alkylaminoesters in high yields without the need for removing a protecting group at the nitrogen atom. Efficient syntheses of pyrrolidines, piperidines, and iminodiacetate derivatives were also developed via tandem N,N- or N, C-dialkylation reactions utilizing characteristics of the silyl substituent. Furthermore, under the influence of silica gel, the addition of an enolate to the imino nitrogen proceeded to give an iminodiacetate derivative.

A facile approach to 2-alkoxyindolin-3-one and its application to the synthesis of N-benzyl matemone

2-Alkoxycarbonylindolin-3-one is synthesized from a methoxyglycine derivative via a 1,2-aza-Brook rearrangement followed by cyclization with bis(trimethylsilyl)aluminum chloride. A short-step synthesis of N-benzyl matemone is successfully carried out using the present indolin-3-one synthesis.

A short-step synthesis of N-benzyl matemone has been successfully carried out using a newly discovered 2-ethoxycarbonylindolin-3-one synthesis.

Umpolung Reaction of α-Imino Thioesters and the Subsequent C-C Bond Formation with the Unexpected Alkylthio Rearrangement

An umpolung reaction of the α-imino thioester was examined, and we found that α-imino thioesters were more effective substrates for the umpolung N-alkylation than conventional α-imino esters and they gave N-alkylated amino thioesters in high yields under mild reaction conditions in a short time. A new type of C-C bond formation followed by an unexpected rearrangement of the alkylthio group took place with the unsaturated ketones to afford the β-alkylthio-α-amino thioesters in high yields with good diastereoselectivity.

Asymmetric synthesis of α-allyl-α-aryl α-amino acids by tandem alkylation/π-allylation of α-iminoesters

The first asymmetric synthesis of α-allyl-α-aryl α-amino acids by means of a three-component coupling of α-iminoesters, Grignard reagents, and cinnamyl acetate is reported. Notably, the enolate from the tandem process provides a much higher level of reactivity and selectivity than the same enolate generated via direct deprotonation, presumably due to differences in the solvation/aggregation state. A novel method for removal of a homoallylic amine protecting group delivers the free amine congeners. The α-allyl group offers a means to generate further valuable α-amino acid structures as exemplified by ring closing metathesis to generate a higher ring homologue of α-aryl-proline.