Catalytic Enantioselective Synthesis of Highly Functionalized Difluoromethylated Cyclopropanes.

The first catalytic asymmetric synthesis of highly functionalized difluoromethylated cyclopropanes is described. The method, based on a rhodium-catalyzed cyclopropanation of difluoromethylated olefins, gives access to a broad range of cyclopropanes bearing ester, ketone, or nitro functional groups. By using Rh2 ((S)-BTPCP)4 as a catalyst, the corresponding products were obtained in high yields and high diastereo- and enantioselectivities (up 20:1 d.r. and 99 % ee). This methodology allowed preparation of enantioenriched difluoromethylcyclopropanes for the first time.

Iridium-catalysed asymmetric allylic alkylation of benzofuran γ-lactones followed by heteroaromatic Cope rearrangement: study of an unusual reaction sequence.

The iridium-catalysed asymmetric allylic alkylation of γ-lactones produces an all-carbon quaternary stereocentre substituted by an allyl and a benzofuran. The resulting 1,5-hexadienes were found to be excellent substrates for an unusual heteroaromatic Cope rearrangement. We describe here the first insight into the synthetic outcome of this intriguing reaction sequence.

Recent Progress Toward the Synthesis of Trifluoromethyl- and Difluoromethyl-Substituted Cyclopropanes.

This Minireview describes recent advances toward the synthesis of trifluoromethyl- and difluoromethyl-substituted cyclopropanes. Synthetic methodologies using [2+1] cycloaddition, ring-contraction, and ring-closure cyclopropanations since 2010 are reported.

Synthesis of chiral γ-lactones by one-pot sequential enantioselective organocatalytic michael addition of boronic acids and diastereoselective intramolecular passerini reaction.

The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential process. The procedure involves an enantioselective organocatalysed transfer of boronic acid to 5-hydroxyfuran-2(5H)-one, followed by an intramolecular diastereoselective Passerini-type reaction. The methodology was developed and optimized with N-Boc-indole-2-boronic acid giving access to α-indole-γ-substituted lactones in high yields and good diastereoisomeric and enantiomeric ratios. By applying the process to other boronic acids, the synthesis of structurally diversified α,γ-substituted chiral lactones was also achieved in good yields albeit with lower enantioselectivities.

Direct synthesis of partially modified 2'-O-pivaloyloxymethyl RNAs by a base-labile protecting group strategy and their potential for prodrug-based gene-silencing applications.

An original and straightforward synthesis of partially modified 2'-O-pivaloyloxymethyl-substituted (PivOM-substituted) oligoribonucleotides has been achieved. The aim of this 2'-enzymolabile modification was to enhance nuclease stability of RNA and transmembrane transport. To make these modified RNAs easily available we developed a base-labile protecting group strategy with standard protections for nucleobases (acyl) and phosphates (cyanoethyl), a Q-linker and two different acetalester protection groups for 2'-OH: propionyloxymethyl (PrOM) and PivOM. Interestingly, orthogonal deprotection conditions based on anhydrous butylamine in THF were found to remove propionyloxymethyl groups selectively, while preserving PivOM groups. Duplex stability, circular dichroism studies and nuclease resistance, as well as the ability to inhibit gene expression of modified 2'-O-PivOM RNA, were evaluated.