Ruthenium-Catalyzed Olefin Cross-Metathesis with Tetrafluoroethylene and Analogous Fluoroolefins

This Communication describes a successful olefin cross-metathesis with tetrafluoroethylene and its analogues. A key to the efficient catalytic cycle is interconversion between two thermodynamically stable, generally considered sluggish, Fischer carbenes. This newly demonstrated catalytic transformation enables easy and short-step synthesis of a new class of partially fluorinated olefins bearing plural fluorine atoms, which are particularly important and valuable compounds in organic synthesis and medicinal chemistry as well as the materials and polymer industries

Functionalized [3 + 3]Cycloalkynes: Substituent Effect on Self-Aggregation by Nonplanar π−π Interactions

Optically active (M)-2,11-dihydroxy-1,12-dimethylbenzo[c]phenanthrene-5,8-dicarbonitrile was synthesized from (M)-1,12-dimethyl-2,11-dinitrobenzo[c]phenanthrene-5,8-dicarbonitrile by the reduction and hydroxylation of nitro groups. The compound was converted to several oxygen-functionalized [3 + 3]cycloalkynes with −OH, −OSiMe2-t-Bu, −OAc, −OTf, or −ONf groups, which are chiral arylene ethynylene macrocycles containing three helicenes. The aggregation behaviors of these [3 + 3]cycloalkynes were examined in CHCl3, THF, and acetone using 1H NMR, CD, and vapor pressure osmometry (VPO) studies and were compared with that of the parent [3 + 3]cycloalkyne. An increasing strength of aggregation in CHCl3 was observed in the following order of the substituted derivatives:  −H > −ONf > −OTf > −OAc > −OSiMe2-t-Bu. In THF the following strength of aggregation was observed:  −OTf > −ONf > −OAc > −H > −OSiMe2-t-Bu > −OH. The aggregation of the functionalized [3 + 3]cycloalkynes is stronger for the compounds with electron-withdrawing substituents than for those with electron-donating substituents. (M)-1,12-dimethylbenzo[c]phenanthrene-2,5,8,11-tetraol was also synthesized from the same intermediate. This electron-rich helicene was readily oxidized to 5,6-quinone in air, and the quinone was suggested to form a self-charge-transfer complex in solid state

Synthesis and Ring Size Effect of Macrocyclic Ethynylhelicene Oligomers

The cyclization of acyclic ethynylhelicene oligomers with decyl 3,5-diiodobenzoate under optimized conditions gave the corresponding optically active [n+n]cycloalkynes (n = 4−8) in high yields. Their structures were compared in terms of ring size by using 1H NMR, UV−vis, and CD spectroscopies and vapor pressure osmometry (VPO). The UV−vis spectra exhibited an increase in absorbance in proportion to n. In contrast, the CD spectra of the macrocycles exhibited a large ring size effect, comparable Δε values despite the increase in n and temperature-dependent properties of the [8+8]cycloalkyne. It was concluded that [4+4]cycloalkyne, [5+5]cycloalkyne, [6+6]cycloalkyne, and [7+7]cycloalkyne have rigid structures, while [8+8]cycloalkyne has a flexible structure

Highly Active Cross-Metathesis of Tetrafluoroethylene with a Seven-Membered N‑Heterocyclic-Carbene–Ruthenium Catalyst

A drastic increase in catalyst turnover number (TON) was accomplished in the cross-metathesis of tetrafluoroethylene (TFE) and vinyl ethers. Under a continuous flow of TFE, catalyst Ru7, which contains a seven-membered N-heterocyclic carbene (NHC) ligand, reached a TON of 4100; this is 2 orders of magnitude higher than the highest hitherto reported value. Mechanistic studies revealed that the expanded NHC successfully destabilizes the stable intermediates with a difluorocarbene structure, which strongly promotes the reaction