Taeboem Oh

Synthesis studies directed toward gelsemine. Preparation of an advanced pentacyclic intermediate

Abstract Pentacyclic gelsemine intermediate 2 was prepared from 3 by a six step sequence whose key steps are (a) intramolecular Mannich cyclization of an N-acyliminium ion intermediate to form the azatricyclo [4.4.0.0 2,8 ] decane ring system, and (b) palladium catalyzed intramolecular alkene arylation to elaborate the spirooxindole.

Asymmetric Diels-Alder reactions in ionic liquids

Abstract Recent interest in ionic liquids has developed various uses for them, including some applications by synthetic chemists. Ionic liquids have joined the potential list of non-traditional solvents for Diels–Alder reactions. We report here our own efforts to examine the rates and selectivities of carbon Diels–Alder reactions. Our investigations show that excellent diastereoselective and enantioselective carbon Diels–Alder reactions can be achieved in imidazolium ionic solvents at room temperature.

Total Synthesis of (±)-Gelsemine

A complex molecular reorganization (1-->2), a sequential anionic aza-Cope rearrangement and Mannich cyclization, and an unprecedented intramolecular Heck reaction of the tetrasubstituted double bond of a vinylogous carbamate are key steps in a new total synthesis of (+/-)-gelsemine (3). MOM=methoxymethyl, DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.

Factors influencing the stereoselectivity in the cycloaddition of imino-dienophiles derived from amino ethers, amino alcohols, and amino acid esters

Abstract Imino dienophiles derived from amino ethers, amino alcohols and amino esters undergo Lewis acid promoted cycloaddition with Danishefskys diene. Cyclic chelation between the imine and oxygen atom increases the stereoselectivity of the reaction.

Chiral Lewis acids derived from 1,8-naphthalenediylbis-(dichloroborane): Mechanistic aspects

Abstract Chiral Lewis acids derived from 1,8-Naphthalenediylbis(dichloroborane), a novel bidentate Lewis acid, have been found to be active catalysts for the asymmetric Diels-Alder reaction. Utilizing chiral ligands derived from amino acids, a range of enantioselectivities have been achieved with cyclopentadiene and various α,β-unsaturated aldehydes. Some mechanistic aspects of this novel asymmetric bidentate catalyst have been addressed.

Simultaneous coordination of 2, 6-dimethylpyranone by 1, 8-naphthalenediylbis(dichloroborane)

Abstract We show evidence of simultaneous coordination of 2, 6-dimethylpyranone by 1, 8-naphthalenediylbis(dichloroborane) in solution.

Chiral Lewis acids derived from 1,8-naphthalenediylbis(dichloroborane)

Abstract Chiral Lewis acids derived from 1,8-Naphthalenediylbis(dichloroborane), a novel bidentate Lewis acid, have been found to be active catalysts for the asymmetric Diels-Alder reaction. Utilizing chiral ligands derived from amino acids and diols, a range of enantioselectivities have been achieved with cyclopentadiene and various α,β-unsaturated aldehydes.

[2,3]-Wittig rearrangement of allylic glycolate esters via boron and tin enolates

Abstract Wittig rearrangement of allylic glycolate esters via boron and tin enolates gave diastereoselectivities as high as 99.5 : 0.5. Tin enolates were more stereoselective than boron enolates.

TOTALSYNTHESE VON ()-GELSEMIN

Eine komplexemolekulareReorganisation (1→2), eine Sequenz aus Aza-Cope-Umlagerung und Mannich-Cyclisierung und eine neuartige intramolekulare Heck-Reaktion der tetrasubstituierten Doppelbindung eines vinylogen Carbamats sind die Schlusselschritte einer neuen Totalsynthese von (±)-Gelsemin 3. MOM=Methoxymethyl, DBU=1,8-Diazabicyclo[5.4.0]undec-7-en.

Synthesis studies directed toward gelsemine. A new synthesis of highly functionalized cis-hydroisoquinolines

Abstract Cis-Hydroisoquinolines can be prepared in good yields by treatment of readily available endo-1-(cyanomethyl)-6-hydroxybicyclo [2.2.2]oct-5-en-1-yl amines with KH as summarized in Scheme 3.