A novel synthesis of β-trifluoromethyl-substituted isoserine via intramolecular rearrangement of imino ethers

Acyclic 1,4-Stereocontrol via the Allylic Diazene Rearrangement: Development, Applications, and the Essential Role of Kinetic E Stereoselectivity in Tosylhydrazone Formation

We report full details of a method for 1,3-reductive transposition of α-alkoxy-α,β-unsaturated hydrazones to provide E-alkenes with high 1,4-stereocontrol between the two respective allylic stereocenters. The process couples a chelation-controlled reduction of the hydrazone with an in situ allylic strain controlled retro-ene reaction of an allyl diazene, i.e., an allylic diazene rearrangement. Such stereotriads are frequently observed motifs in natural products. We observed a fortuitous kinetic preference for the E-hydrazone geometry during the hydrazonation reaction, as only the E-isomers could undergo chelation-controlled reduction.

Exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology

Over the last three decades, my engagement in "fluorine chemistry" has evolved substantially because of the multidisciplinary nature of the research programs. I began my research career as a synthetic chemist in organometallic chemistry and homogeneous catalysis directed toward organic synthesis. Then, I was brought into a very unique world of "fluorine chemistry" in the end of 1970s. I started exploring the interface of fluorine chemistry and transition metal homogeneous catalysis first, which was followed by amino acids, peptides, and peptidomimetics for medicinal chemistry. Since then, I have been exploring the interfaces of fluorine chemistry and multidisciplinary fields of research involving medicinal chemistry, chemical biology, cancer biology, and molecular imaging. This perspective intends to cover my fruitful endeavor in the exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology in a chronological order to show the evolution of my research interest and strategy.

Diastereoselective synthesis of S-tert-butyl-beta-(trifluoromethyl)isocysteine

Both diastereoisomers of S-tert-butyl-beta-(trifluoromethyl)isocysteine have been synthesized stereoselectively by the sequential reactions of trifluoroacetimidoyl chloride with the lithium enolate of tert-butyl alpha-tert-butylthioacetate, followed by the diastereoselective reduction of the imino group with sodium borohydride in the presence of zinc(II) or di(ethylene glycol) dimethyl ether, and finally by the deprotection of N-aryl and tert-butyl ester groups.

(R)-Trifluoro- and Difluoropyruvaldehyde N,S-Ketals: Chiral Synthetic Equivalents of beta-Trifluoro and beta-Difluoro alpha-Amino Aldehydes

A new, efficient, and stereoselective two-step approach to stereochemically defined chiral nonracemic gamma-tri- and gamma-difluoro beta-amino alcohols (70% to >95% ee) is described, using tri- and difluoropyruvaldehyde N,S-ketals (R)-1a,b as starting materials. Addition of Grignard reagents to (R)-1 occurs with moderate to excellent anti-stereocontrol, depending on the nature of the organomagnesium halides, providing the beta-p-tolylthio beta-benzyloxycarbonylamino secondary carbinols 5. The stereochemical outcome of these reactions can be rationalized by means of a chelated Cram's cyclic model, where the NCbz group is the chelating ligand and the p-tolylthio residue acts as the stereocontrolling "large" group. Reductive displacement of the 2-p-tolylthio substituent of 5 efficiently takes places by means of the NaBH(4)/pyridine system, probably via the corresponding intermediate transient imines 13, providing sulfur-free gamma-tri- and gamma-difluorinated beta-amino alcohols 7 with high levels of anti-stereoselectivity. A considerable shift toward syn-stereoselectivity was obtained performing the reaction on the corresponding phenylacetates 8. Cleavage and reduction of the NHCbz moiety of 7 provided tri- and difluoro analogues of, respectively, norephedrine (11) and ephedrine (12).