Stereoselective Synthesis of the C1−C11 and C12−C34 Fragments of Mycalolide A

Reiterative epoxide-based strategies for the synthesis of stereo-n-ads and application to polypropionate synthesis. A Personal Account

The enantioselective synthesis of polypropionates continues to be an attractive realm for the synthetic chemists mostly due to the challenges presented by the number of consecutive stereogenic centers contained within the aliphatic chain. Over the years, our laboratory has developed an epoxide-based three-step reiterative methodology for the construction of these targets, with the ultimate goal that the approach could be extended to the synthesis of polypropionate-containing natural products. The key steps include the diastereoselective epoxidation of allylic and homoallylic alcohols, and the regioselective cleavage of 2-methyl-3,4-epoxy alcohols. The choice of the organometallic reagent, and the cis/trans geometry of the chiral epoxide can be used to control both the relative and absolute configuration of the resulting propionate unit, allowing our approach to be applied in the synthesis of advanced fragments. Additionally, the combination of our first- and second-generation methodologies permits the incorporation of different variations at the methyl moiety.

Solution-phase automated synthesis of an α-amino aldehyde as a versatile intermediate

A solution-phase automated synthesis of the versatile synthetic intermediate, Garner's aldehyde, was demonstrated. tert-Butoxycarbonyl (Boc) protection, acetal formation, and reduction of the ester to the corresponding aldehyde were performed utilizing our originally developed automated synthesizer, ChemKonzert. The developed procedure was also useful for the synthesis of Garner's aldehyde analogues possessing fluorenylmethyloxycarbonyl (Fmoc) or benzyloxycarbonyl (Cbz) protection.

The synthesis and biological evaluation of a kabiramide C fragment modified with a WH2 consensus actin-binding motif as a potential disruptor of the actin cytoskeleton

Despite its low affinity for actin monomers, a fragment of kabiramide C disrupts actin filamentsin vitroand in cells.

Crystal structure of 4-tert-butyl-2-{2-[N-(3,3-dimethyl-2-oxobut-yl)-N-iso-propyl-carbamo-yl]phen-yl}-1-isopropyl-1H-imidazol-3-ium perchlorate

In the title salt, C26H40N3O2 (+)·ClO4 (-), the positive charge of the organic cation is delocalized between the two N atoms of the imidazole ring. The C N bond distances are 1.338 (2) and 1.327 (3) Å. The substituents on the benzene ring are rotated almost orthogonal with respect to this ring due to the presence of the bulky isopropyl substituents. The dihedral angle between the benzene and imidazole rings is 75.15 (12)°. Three of the O atoms of the anion are disordered over two sets of sites due to rotation around one of the O-Cl bonds. The ratio of the refined occupancies is 0.591 (14):0.409 (14). In the crystal, the cation and perchlorate anion are bound by an N-H⋯O hydrogen bond. In addition, the cation-anion pairs are linked into layers parallel to (001) by multiple weak C-H⋯O hydrogen bonds.

Diastereo- and enantioselective synthesis of 1,3,5,7-tetraol structural units using a Prins cyclisation–reductive cleavage sequence

Stereocontrolled access to all the diastereomers of 1,3,5,7-tetraol structural units was developed using a Prins cyclisation–reductive cleavage sequence.

Cooperative titanocene and phosphine catalysis: accelerated C-X activation for the generation of reactive organometallics

The study presented herein describes a reductive transmetalation approach toward the generation of Grignard and organozinc reagents mediated by a titanocene catalyst. This method enables the metalation of functionalized substrates without loss of functional group compatibility. Allyl zinc reagents and allyl, vinyl, and alkyl Grignard reagents were generated in situ and used in the addition to carbonyl substrates to provide the corresponding carbinols in yields up to 99%. It was discovered that phosphine ligands effectively accelerate the reductive transmetalation event to enable the metalation of C-X bonds at temperatures as low as -40 °C. Performing the reactions in the presence of chiral diamines and amino alcohols led to the enantioselective allylation of aldehydes.

Organocatalyzed enantioselective desymmetrization of diols in the preparation of chiral building blocks

Desymmetrization of diols is a powerful tool to the synthesis of chiral building blocks. Among the different approaches to perform discrimination between both enantiotopic hydroxyl groups, the organocatalytic approach has gained importance in the last years. A diverse range of organocatalysts has been used to efficiently promote this enantioselective transformation and this Minireview examines the different contributions in this field.

Enantioselective synthesis of Garner's aldehyde by asymmetric hydroformylation

Both enantiomers of Garner's aldehyde (3) are prepared from the same alkene 4 by catalytic asymmetric hydroformylation.