Enantio- and Diastereoselective Aldol-Reaction of 2,6-Dimethylphenyl Propionate Using Titanium-Carbohydrate Complexes

Intramolecular Diels-Alder (IMDA) Studies toward the Synthesis of Australifungin. Stereocontrol in the Acetate Aldol Reaction of β,β'-Branched Aldehydes

Studies of australifungin illustrate an enantiocontrolled synthesis of the trans-decalin core 28 via an intramolecular [4π + 2π] cycloaddition. This strategy utilizes the nitroalkene dienophile of 27 as a surrogate ketene equivalent. Stereocontrol at C-2 is critically important for an effective intramolecular Diels-Alder (IMDA) process. Our studies report high asymmetric induction using a nonracemic Duthaler titanium enolate in the acetate aldol reaction with β,β'-branched aldehyde 13 to introduce the required C-2 chirality.

Synthesis of two bioactive natural products: FR252921 and pseudotrienic acid B

Concise and highly convergent syntheses of the immunosuppressive agent FR252921 and the related antimicrobial natural product pseudotrienic acid B were achieved from a common intermediate by using optically active titanium complexes to control the configuration of the stereogenic centers, a highly stereo- and regioselective cross-metathesis to generate the triene moieties, and a Stille cross-coupling to install the dienic units.

Carbohydrates as Synthetic Tools in Organic Chemistry

While amino acids, terpenes and alkaloids have found broad application as tools in stereoselective organic synthesis, carbohydrates have only lately been recognised as versatile starting materials for chiral auxiliaries, reagents, ligands and organocatalysts. The structural diversity of carbohydrates and the high density of functional groups offer a wide variety of opportunities for derivatization and tailoring of synthetic tools to a specific problem.

Chelation-controlled ester-derived titanium enolate aldol reaction: diastereoselective syn-aldols with mono- and bidentate aldehydes

A chelation-controlled and highly diastereoselective synthesis of syn-aldols is described. Aldol reaction of (S)-valinol-derived ester with a variety of aldehydes proceeded with high syn-diastereoselectivities (up to 99:1) and isolated yields (94%).

Ester derived titanium enolate aldol reaction: chelation controlled diastereoselective synthesis of syn-aldols

A chelation controlled and highly diastereoselective synthesis of syn-aldols is described. Aldol reaction of commercially available L-phenylalaninol derived esters with a variety of bidentate oxyaldehydes proceeded with excellent syn-diastereoselectivities and isolated yields.

ESTER DERIVED TITANIUM ENOLATE ALDOL REACTION: HIGHLY DIASTEREOSELECTIVE SYNTHESIS OF SYN- AND ANTI-ALDOLS

Aldol reactions of bidentate aldehydes and cis-1-arylsulfonamido-2-indanyl ester derived titanium enolates proceed with excellent syn-diastereoselectivities and good to excellent isolated yields.

Total Synthesis of the Serine/Threonine-Specific Protein Phosphatase Inhibitor Tautomycin(1)

A convergent, asymmetric synthesis of the protein phosphatase inhibitor, tautomycin, is described. The natural product was constructed by joining two major fragments of comparable complexity at the C21-C22 bond. Absolute stereochemistry of the C1-C21 ketone originates from (S)-citronellene and (2R,3S)-geraniol epoxide. The anti stereochemical relationships at C6-C7 and C18-C19 were introduced with Duthaler's chiral titanium propionic enolate. Syn stereochemical relationships at C13-C14 and C23-C24 were established using an Evan's oxazolidinone chiral auxiliary. The spiroketal was efficiently constructed via a one-pot double-alkylation-spirocyclization sequence with acetone N,N-dimethylhydrazone serving as the central linchpin. Final coupling of the two halves using a chelation-controlled Mukaiyama aldol addition followed by deprotection yielded synthetic tautomycin that is identical to the natural product.