This
study describes the development and understanding of a palladium-catalyzed
cross-coupling of fluoroacetamides with boronic acids, under base-free
conditions, to selectively give valuable α,α-difluoroketone
derivatives. Detailed mechanistic studies were conducted to assess
the feasibility of each elementary step, that is, C(acyl)–N
bond oxidative addition, followed by base-free transmetallation and
reductive elimination. These investigations allowed the structural
characterization of palladium(II)fluoroacyl intermediates derived
from C–N bond oxidative addition of an amide electrophile.
They also revealed the high reactivity of these intermediates for
transmetallation with boronic acids without exogenous base. The mechanistic
studies also provided a platform to design a practical catalytic protocol
for the synthesis of a diversity of α,α-difluoroketones,
including CF2H–ketones. Finally, the synthetic potential
of this fluoroacylation methodology is highlighted in sequential,
orthogonal C–Br and C–N bond functionalization of an
α-bromo-α,α-difluoroacetamide with a focus on compounds
of potential biological relevance.
Herein, a straightforward synthesis of thiocarbamoyl fluorides is reported starting from amines and carbon disulfide. The key to success is the fluorinative desulfurization of carbon disulfide with (diethylamino)sulfur trifluoride (DAST). The title compounds were obtained in moderate to very good isolated yields. Furthermore, we demonstrated also that thiocarbamoyl fluoride can be converted into their trifluoromethylamine analogues through simple treatment with silver fluoride.
Herein, a new concept for the direct synthesis of carbamoyl fluoride derivatives is disclosed. The developed method makes use of CO2 as an inexpensive and abundant C1 source; a variety of amines were successfully converted in the presence of a deoxyfluorinating reagent. The corresponding products were often obtained in excellent yields under mild reaction conditions (1 atm and room temperature). The reaction was easily scaled up, demonstrating the efficiency of the developed process.
A range of thermomorphic polyethylene‐supported organocatalysts is prepared from N‐alkyl imidazoles and polyethylene iodide (PEI) with good yields (85–92%) and high funtionality (98–99%). The catalytic activity of these species is studied for the ring opening of epoxidized methyl oleate with CO2 to give the corresponding cyclic carbonate. The reaction is carried out at 100 °C to fully exploit the thermomorphic behavior of the organocatalysts. The optimized conditions (neat, 100 °C, and 20 bar of CO2) are applied to a range of epoxidized fatty acids, including an epoxidized rapeseed oil, to give the corresponding carbonates with good yields (75–96%). The catalyst recycling is also studied, and no significant loss of activity is observed after ten runs. The fatty carbonates are important intermediates for the preparation of non‐isocyanate polyurethanes (NIPUs).
The organocatalytic synthesis of substituted vinylene carbonates from benzoins and acyloins was studied using diphenyl carbonate as a carbonyl source. A range of N‐Heterocyclic Carbene (NHC) precursors were screened and it was found that imidazolium salts were the most active for this transformation. The reaction occurs at 90 °C under solvent‐free conditions. A wide range of substituted vinylene carbonates (symmetrical and unsymmetrical, aromatic or aliphatic), including some derived from natural products, were prepared with 20–99% isolated yields (24 examples). The reaction was also developed using thermomorphic polyethylene‐supported organocatalysts as recoverable and recyclable species. The use of such species facilitates the workup and allows the synthesis of vinylene carbonates on the preparative scale (>30 g after 5 runs).
An imidazolium catalyst supported on thermomorphic polyethylene (PE) was prepared from 1methylimidazole and polyethylene iodide (PEÀ I). The catalyst was characterized by 1 H and 13 C NMR, SEC and MALDI-ToF mass spectrometry. Its catalytic activity was evaluated in the ring-opening of epoxides with carbon dioxide to give cyclic carbonates under solvent-free conditions. The catalyst proved to be active at low catalyst loading (down to 0.1 mol%) and allows the reaction to occur at low CO 2 pressure (1-5 bar) and moderate temperature (100°C). A range of terminal and internal epoxides was converted to the corresponding cyclic carbonates with high yields and selectivities. The recyclability of the catalyst was studied and no significant loss of activity was observed after 5 runs.
Substituted vinylene carbonates were directly prepared from aromatic aldehydes following a one‐pot Benzoin condensation/transcarbonation sequence under solvent‐free conditions. The combination of a N‐phenyl substituted triazolium salt NHC precursor and 4‐dimethylaminopyridine (DMAP) was found essential to reach high yield and selectivity. The reaction scope was investigated with a range of aromatic aldehydes and the corresponding vinylene carbonates were obtained with 32–86 % isolated yields (14 examples).
Substituted vinylene carbonates were directly prepared from aromatic aldehydes following a one-pot Benzoin condensation / transcarbonation sequence under solvent-free conditions. The combination of a N-phenyl substituted triazolium salt NHC precursor and 4-dimethylaminopyridine (DMAP) was found essential to reach high yield and selectivity. The reaction scope was investigated with a range of aromatic aldehydes and the corresponding vinylene carbonates were obtained with 32-86% isolated yields (14 examples).
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