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The 2H‐tetrahydro‐4,6‐dioxo‐1,2‐oxazine (TDO) ring, a rare structural motif embedded in the molecular architecture of alchivemycins, is synthesized from 2,2,6‐trimethyl‐4H‐1,3‐dioxin‐4‐one via two routes. Both routes involve the intramolecular trapping of an acylketene intermediate by an internal hydroxy group to form the TDO ring as a key step. The first synthesis was achieved in 29 % overall yield from the starting material by a four‐step sequence featuring a DMAP−CaCl2‐mediated O‐ to C‐acyl migration reaction to install an acyl group at the C5 position of the TDO ring. The second synthesis was completed in 8 % overall yield from the same starting material as the first one through five steps by exploiting a photo‐induced double bromination reaction. [ABSTRACT FROM AUTHOR]

We developed a route to rhodomyrtone analogs that feature different acyl groups at C7. Since electrophilic substitution reactions on the aryl part of the rhodomyrtone core led to C5 derivatives, the C5 position was blocked by a chlorine. Subsequent Duff type formylation followed by Grignard addition to the aldehyde group and oxidation gave various phenones. The benzyl protecting groups were removed by hydrogenation or boron tribromide. Some derivatives turned out to be quite active against multiple resistant Staphylococcus aureus strains and a rhodomyrtone resistant mutant (RomR). The chlorine at C5 seems to have a beneficial effect on the antibacterial activity. [ABSTRACT FROM AUTHOR]

A photochemical cyclization of F‐tagged, o‐alkynylated N‐alkylamides to indoles catalyzed by [Ir(dF(CF3)ppy)2(dtbpy)]PF6 is presented. This straightforward and efficient reaction involves an intramolecular rearrangement due to the presence of an electron withdrawing group in the acyl moiety and is the first example of photochemically induced 1,3‐acyl shift in the cyclization towards 3‐acylindoles. A four‐step reaction sequence including the photoreaction as a key step to the desired indoles has been developed and optimized. The compatibility of differently substituted F‐tagged precursors with the photocyclization step was investigated and the robustness of this step towards modifications could be shown. In total, 16 so far unknown derivatives with diverse modifications in positions N1 and C2, bearing a pentadecafluorooctanoyl moiety as F‐tag, were synthesized in very good yields and fully characterized. [ABSTRACT FROM AUTHOR]

Fluorination is a potent method to modulate chemical properties of glycans. Here, we study how C3‐ and C6‐fluorination of glucosyl building blocks influence the structure of the intermediate of the glycosylation reaction, the glycosyl cation. Using a combination of gas‐phase infrared spectroscopy and first‐principles theory, glycosyl cations generated from fluorinated and non‐fluorinated monosaccharides are structurally characterized. The results indicate that neighboring group participation of the C2‐benzoyl protecting group is the dominant structural motif for all building blocks, correlating with the β‐selectivity observed in glycosylation reactions. The infrared signatures indicate that participation of the benzoyl group in enhanced by resonance effects. Participation of remote acyl groups such as Fmoc or benzyl on the other hand is unfavored. The introduction of the less bulky fluorine leads to a change in the conformation of the ring pucker, whereas the structure of the active dioxolenium site remains unchanged. [ABSTRACT FROM AUTHOR]

Pyridinium 1,4‐zwitterionic thiolates as a class of sulfur‐containing synthons were applied to a [3+2] cascade cyclization reaction with activated alkynes, affording a library of polysubstituted thiophenes with excellent regioselectivities, especially those bearing various fluorine‐containing groups. The freshly disclosed pyridinium 1,4‐zwitterionic thiolates decorated with acyl or trifluoromethyl groups exhibited powerful potential in the synthesis of polysubstituted thiophenes. Of particular note is that pyridinium A4 could introduce sulfur and CF3 groups to target products simultaneously. [ABSTRACT FROM AUTHOR]

The synthesis of both regioisomers of monoacylated diols has been achieved in one simple step using a Passerini reaction. We examined various substrates and reaction conditions, and the results show that the regioselectivity of the reaction is governed by a choice between five‐ and six‐membered‐ring transition states, and by different rates of acyl migration under different reaction conditions. [ABSTRACT FROM AUTHOR]

We report a 5-step sequence for the synthesis of phosphatidylglycerols (PG) bearing different or identical chains at positions sn-1 and sn-2 starting from phenyl dichlorophosphate and using (S)-glycidol as the chiral source. Overall, this new approach is more convergent that the previously reported syntheses as the PG derivatives are constructed around the phosphorus center. Hence, this method is more convenient for the incorporation of expensive or complex acyl chains at the sn-2 position. [ABSTRACT FROM AUTHOR]

In the preparation of multicomponent compounds, the accumulation of components through sequential click reactions is an attractive strategy. In this work we examined the reactivity of various N-substituted 7-azanorbornenes in inverse electron-demand Diels-Alder (iEDDA) reactions with tetrazines to explore the potential of 7-azanorbornenes as clickable hub molecules. The iEDDA reaction of 7-azanorbornene is expected to proceed faster when the nitrogen atom at the 7-position is substituted with an electron-donating substituent. Contrary to this expectation, the electron-donating alkyl-bearing derivative reacted much more slowly than those bearing electron-withdrawing acyl groups. The results of DFT calculations indicate that the reaction rates correlate well with an increase in sp2 character of the 7-nitrogen atoms: The ease of conversion of the more stable exo conformer into the more reactive endo conformer may lower the activation energy of the first rate-determining hetero-Diels-Alder step. Indeed, the reaction rates of N-acylated 7-azanorbornenes, which have a more planar nitrogen atom, were found superior to those of other derivatives and comparable to those of norbornenes. Finally, we successfully labeled a tetrazine on a protein surface by fluorophore-conjugated 7-azanorbornene in the presence of other proteins. [ABSTRACT FROM AUTHOR]

A family of stabilized münchnones bearing an acyl group at C4 have been prepared and studied in alkyne cycloaddition reactions. These reactions are highly regioselective, and the method represents a rapid and straightforward route to densely substituted pyrroles. Finally, the C4-stabilizing units can be further manipulated to furnish carboxylic acid and amide groups, or removed altogether to provide unsubstituted pyrroles. [ABSTRACT FROM AUTHOR]

Diverse chromenones were synthesized through tunable phosphine-mediated cascade reactions between 3-acyl-2 H-chromen-2-ones and Morita-Baylis-Hillman (MBH) derivatives. With different phosphine loadings and reaction temperatures, MBH derivatives act either as C1 or C3 synthons for the construction of potential biologically active 3-dihydrofuran-fused chromen-2-ones, 4-allyl-3-acyl-chromen-2-ones, or 6 H-benzo[ c]chromen-6-ones. This method has the advantages of mild conditions, simple workup, and wide substrate scope, which make it powerful for the synthesis of diverse chromenone derivatives. [ABSTRACT FROM AUTHOR]