Birch-Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer.

The direct reduction of arenes and heteroarenes by visible-light irradiation remains challenging, as the energy of a single photon is not sufficient for breaking aromatic stabilization. Shown herein is that the energy accumulation of two visible-light photons allows the dearomatization of arenes and heteroarenes. Mechanistic investigations confirm that the combination of energy-transfer and electron-transfer processes generates an arene radical anion, which is subsequently trapped by hydrogen-atom transfer and finally protonated to form the dearomatized product. The photoreduction converts planar aromatic feedstock compounds into molecular skeletons that are of use in organic synthesis.

Histone deacetylase inhibitor treatment dramatically reduces cholesterol accumulation in Niemann-Pick type C1 mutant human fibroblasts.

Niemann-Pick type C (NPC) disease is predominantly caused by mutations in the NPC1 protein that affect intracellular cholesterol trafficking and cause accumulation of unesterified cholesterol and other lipids in lysosomal storage organelles. We report the use of a series of small molecule histone deacetylase (HDAC) inhibitors in tissue culture models of NPC human fibroblasts. Some HDAC inhibitors lead to a dramatic correction in the NPC phenotype in cells with either one or two copies of the NPC1(I1061T) mutation, and for several of the inhibitors, correction is associated with increased expression of NPC1 protein. Increased NPC1(I1061T) protein levels may partially account for the correction of the phenotype, because this mutant can promote cholesterol efflux if it is delivered to late endosomes and lysosomes. The HDAC inhibitor treatment is ineffective in an NPC2 mutant human fibroblast line. Analysis of the isoform selectivity of the compounds used implicates HDAC1 and/or HDAC2 as likely targets for the observed correction, although other HDACs may also play a role. LBH589 (panobinostat) is an orally available HDAC inhibitor that crosses the blood-brain barrier and is currently in phase III clinical trials for several types of cancer. It restores cholesterol homeostasis in cultured NPC1 mutant fibroblasts to almost normal levels within 72 h when used at 40 nM. The findings that HDAC inhibitors can correct cholesterol storage defects in human NPC1 mutant cells provide the potential basis for treatment options for NPC disease.

B-(3,3-difluoroallyl)diisopinocampheylborane for the enantioselective fluoroallylboration of aldehydes.

The fluoroallylboration of aldehydes with B-(3,3-difluoroallyl)diisopinocampheylborane, which was prepared via the hydroboration of 1,1-difluoroallene, provides chiral 2,2-gem-difluorinated homoallylic alcohols in good yields and 91-97% ee.

Generation and trapping of a cage annulated vinylidenecarbene and approaches to its cycloalkyne isomer.

A novel cage-annulated (bis-homocubyl) vinylidenecarbene has been generated and successfully trapped without any intermediacy of its cycloalkyne isomer. The greater kinetic and thermodynamic stability of the vinylidenecarbene vis-à-vis its cycloalkyne isomer has been predicted by DFT B3LYP/6-31G* calculations. The calculated results suggest the prospects of the cycloalkyne becoming amenable for trapping, if generated under suitable experimental conditions, owing to the substantial kinetic energy barrier associated with its possible ring contraction via 1,2-shift to the vinylidenecarbene isomer and marginal ground state energy difference. However, all of our attempts to directly generate and trap the cycloalkyne yielded unsatisfactory results. Attempted generation and trapping of a C2-symmetric bis-vinylidenecarbene from a bis-vinylidenedibromide met with unexpected failure.

Visible light induced redox neutral fragmentation of 1,2-diol derivatives.

A homogeneous, redox-neutral photo fragmentation of diol derivatives was developed. Under photo/hydrogen atom transfer (HAT) dual catalysis, diol derivatives such as lignin model compounds and diol monoesters undergo selective ß C(sp3)-O bond cleavage to afford ketones, phenols and acids effectively.

Gem-difluorinated homoallyl alcohols, beta-hydroxy ketones, and syn- and anti-1,3-diols via gamma,gamma-difluoroallylboronates.

Gamma,gamma-difluoroallylboronates have been prepared from trifluoroethanol and utilized for the allylboration of a variety of aldehydes to provide gem-difluorinated homoallylic alcohols. Alpha-chiral aldehydes were allylborated in 4:1-13:1 diastereoselectivity favoring the anti-isomer. A representative series of difluorinated hydroxyl enol ethers were converted to the corresponding alpha,alpha-difluoro-beta-hydroxy ketones. Diastereoselective reduction of one of these to either syn- and anti-1,3-diol was also studied.

An enantioselective artificial Suzukiase based on the biotin-streptavidin technology.

Introduction of a biotinylated monophosphine palladium complex within streptavidin affords an enantioselective artificial Suzukiase. Site-directed mutagenesis allowed the optimization of the activity and the enantioselectivity of this artificial metalloenzyme. A variety of atropisomeric biaryls were produced in good yields and up to 90% ee. The hybrid catalyst described herein shows comparable TOF to the previous aqueous-asymmetric Suzuki catalysts, and excellent stability under the reaction conditions to realize higher TON through longer reaction time.

Fluoroallylboration-olefination for the synthesis of (Z)-4,4-difluoropent-2-enoates and 5,5-difluoro-5,6-dihydropyran-2-ones.

Horner-Wadsworth-Emmons (HWE) or Still-Gennari olefination of TBS-protected 3,3-difluoro-4-hydroxy-2-ones, derived from the difluoroallylboration of aldehydes, provides the Z-isomer of 4,4,-difluoropent-2-enoates. These, upon hydrolysis, followed by Yamaguchi cyclization, afford 5,5-difluoro-4-methyl-5,6-dihydro-α-pyrones in high yields.

An efficient synthesis of (+/-)-trichostatic Acid and analogues: a new route to (+/-)-trichostatin A.

An efficient synthesis of rac-trichostatic acid (1) and its analogues is reported starting from a commercially available aldehyde. Further manipulations of rac-1 led to rac-trichostatin A (TSA). Construction of the desired molecular architecture entails a two-component union, achieved through an in situ hydroboration followed by a Suzuki-Miyaura coupling with 2. The requisite homopropargyl alcohol was synthesized by exploiting allenylindium chemistry. This new protocol paved the way for the synthesis of analogues of trichostatic acid and hence TSA.